diff --git a/public/popup.css b/public/popup.css
index 986e745..57a2253 100644
--- a/public/popup.css
+++ b/public/popup.css
@@ -331,3 +331,182 @@ body {
 .confirm-buttons .btn {
   flex: 1;
 }
+
+/* 주기 선택 드롭다운 */
+.cycle-select {
+  width: 100%;
+  padding: 10px 12px;
+  border: 1px solid #ddd;
+  border-radius: 6px;
+  font-size: 14px;
+  background-color: #fff;
+  cursor: pointer;
+  transition: border-color 0.2s;
+}
+
+.cycle-select:focus {
+  outline: none;
+  border-color: #3498db;
+}
+
+/* 주기 목록 */
+.cycle-list {
+  list-style: none;
+  margin-top: 12px;
+  margin-bottom: 12px;
+}
+
+.cycle-item {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 10px;
+  margin-bottom: 8px;
+  background-color: #f8f9fa;
+  border-radius: 6px;
+}
+
+.cycle-item-empty {
+  padding: 12px;
+  text-align: center;
+  color: #95a5a6;
+  font-size: 12px;
+}
+
+.cycle-info {
+  flex: 1;
+  min-width: 0;
+}
+
+.cycle-title {
+  font-weight: 500;
+  font-size: 13px;
+  margin-bottom: 2px;
+}
+
+.cycle-durations {
+  font-size: 11px;
+  color: #7f8c8d;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.cycle-actions {
+  display: flex;
+  gap: 4px;
+  margin-left: 8px;
+}
+
+.btn-small {
+  padding: 6px 10px;
+  font-size: 12px;
+  width: auto;
+}
+
+/* 모달 */
+.modal {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background-color: rgba(0, 0, 0, 0.5);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 200;
+}
+
+.modal-content {
+  background: #fff;
+  padding: 20px;
+  border-radius: 8px;
+  width: 290px;
+  max-height: 90vh;
+  overflow-y: auto;
+}
+
+.modal-content h3 {
+  margin-bottom: 16px;
+  font-size: 16px;
+  color: #2c3e50;
+}
+
+/* Duration 입력 그룹 */
+.duration-input-group {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  margin-bottom: 8px;
+}
+
+.duration-value {
+  width: 60px;
+  padding: 8px;
+  border: 1px solid #ddd;
+  border-radius: 4px;
+  font-size: 14px;
+  text-align: center;
+}
+
+.duration-value:focus {
+  outline: none;
+  border-color: #3498db;
+}
+
+.duration-unit {
+  padding: 8px;
+  border: 1px solid #ddd;
+  border-radius: 4px;
+  font-size: 14px;
+  background-color: #fff;
+  cursor: pointer;
+}
+
+.duration-unit:focus {
+  outline: none;
+  border-color: #3498db;
+}
+
+.btn-remove-duration {
+  width: 28px;
+  height: 28px;
+  padding: 0;
+  border: none;
+  border-radius: 4px;
+  background-color: #e74c3c;
+  color: #fff;
+  font-size: 16px;
+  cursor: pointer;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.btn-remove-duration:hover {
+  background-color: #c0392b;
+}
+
+/* 폼 버튼 영역 */
+.form-actions {
+  display: flex;
+  gap: 8px;
+  margin-top: 16px;
+}
+
+.form-actions .btn {
+  flex: 1;
+}
+
+/* 주기 섹션 */
+#cycle-section {
+  margin-top: 12px;
+  margin-bottom: 12px;
+}
+
+#cycle-section h3 {
+  font-size: 14px;
+  margin-bottom: 8px;
+  color: #2c3e50;
+}
diff --git a/public/popup.html b/public/popup.html
index 60f7628..ad77867 100644
--- a/public/popup.html
+++ b/public/popup.html
@@ -38,6 +38,14 @@ <h1>Recycle Study</h1>
         <span id="user-email"></span>
       </div>
 
+      <!-- 복습 주기 선택 -->
+      <div class="form-group">
+        <label for="cycle-select">복습 주기</label>
+        <select id="cycle-select" class="cycle-select">
+          <!-- 동적으로 옵션 추가 -->
+        </select>
+      </div>
+
       <button id="save-url-btn" class="btn btn-primary btn-large">
         현재 페이지 저장
       </button>
@@ -52,6 +60,16 @@ <h1>Recycle Study</h1>
 
       <hr class="divider">
 
+      <!-- 주기 관리 버튼 -->
+      <button id="cycle-manage-btn" class="btn btn-secondary">복습 주기 관리</button>
+
+      <!-- 주기 관리 섹션 -->
+      <div id="cycle-section" class="hidden">
+        <h3>나의 복습 주기</h3>
+        <ul id="cycle-list" class="cycle-list"></ul>
+        <button id="cycle-add-btn" class="btn btn-secondary btn-small">+ 새 주기 추가</button>
+      </div>
+
       <button id="show-devices-btn" class="btn btn-secondary">디바이스 관리</button>
 
       <div id="devices-section" class="hidden">
@@ -71,6 +89,30 @@ <h3>등록된 디바이스</h3>
     </div>
   </div>
 
+  <!-- 주기 폼 모달 -->
+  <div id="cycle-modal" class="modal hidden">
+    <div class="modal-content">
+      <h3 id="cycle-modal-title">새 복습 주기</h3>
+      <form id="cycle-form">
+        <div class="form-group">
+          <label for="cycle-title-input">주기 이름</label>
+          <input type="text" id="cycle-title-input" placeholder="예: 시험 대비 단기 암기">
+        </div>
+        <div class="form-group">
+          <label>복습 간격 (등록 시점 기준)</label>
+          <div id="cycle-durations-container">
+            <!-- 동적으로 추가 -->
+          </div>
+          <button type="button" id="add-duration-btn" class="btn btn-text btn-small">+ 간격 추가</button>
+        </div>
+        <div class="form-actions">
+          <button type="button" id="cycle-form-cancel" class="btn btn-secondary">취소</button>
+          <button type="submit" id="cycle-form-submit" class="btn btn-primary">저장</button>
+        </div>
+      </form>
+    </div>
+  </div>
+
   <script type="module" src="popup.js"></script>
 </body>
 </html>
diff --git a/src/__tests__/api.test.js b/src/__tests__/api.test.js
index 7ba2ebe..b9f6e55 100644
--- a/src/__tests__/api.test.js
+++ b/src/__tests__/api.test.js
@@ -1,5 +1,14 @@
 import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
-import { registerDevice, getDevices, deleteDevice, saveReviewUrl } from '../api.js';
+import {
+  registerDevice,
+  getDevices,
+  deleteDevice,
+  saveReviewUrl,
+  getCycleOptions,
+  createCustomCycle,
+  updateCustomCycle,
+  deleteCustomCycle
+} from '../api.js';
 import { ERROR_CODES } from '../constants.js';
 
 // Mock chrome.runtime.sendMessage
@@ -79,13 +88,14 @@ describe('api.js', () => {
   });
 
   describe('saveReviewUrl', () => {
-    it('식별자를 헤더에 포함하여 URL 저장 요청을 보낸다', async () => {
+    it('식별자와 주기를 포함하여 URL 저장 요청을 보낸다', async () => {
       const identifier = 'my-device-id';
       const targetUrl = 'https://example.com';
-      const mockResponse = { success: true, data: { url: targetUrl } };
+      const cycle = { type: 'DEFAULT', code: 'EBBINGHAUS' };
+      const mockResponse = { success: true, data: { url: targetUrl, scheduledAts: [] } };
       sendMessageMock.mockResolvedValue(mockResponse);
 
-      await saveReviewUrl(identifier, targetUrl);
+      await saveReviewUrl(identifier, targetUrl, cycle);
 
       expect(sendMessageMock).toHaveBeenCalledWith({
         type: 'API_REQUEST',
@@ -93,7 +103,120 @@ describe('api.js', () => {
           endpoint: '/api/v1/reviews',
           method: 'POST',
           headers: { 'X-Device-Id': identifier },
-          body: { targetUrl }
+          body: { targetUrl, cycle }
+        }
+      });
+    });
+
+    it('커스텀 주기로 URL 저장 요청을 보낸다', async () => {
+      const identifier = 'my-device-id';
+      const targetUrl = 'https://example.com';
+      const cycle = { type: 'CUSTOM', id: 1 };
+      const mockResponse = { success: true, data: { url: targetUrl, scheduledAts: [] } };
+      sendMessageMock.mockResolvedValue(mockResponse);
+
+      await saveReviewUrl(identifier, targetUrl, cycle);
+
+      expect(sendMessageMock).toHaveBeenCalledWith({
+        type: 'API_REQUEST',
+        request: {
+          endpoint: '/api/v1/reviews',
+          method: 'POST',
+          headers: { 'X-Device-Id': identifier },
+          body: { targetUrl, cycle }
+        }
+      });
+    });
+  });
+
+  describe('getCycleOptions', () => {
+    it('주기 옵션 목록을 조회한다', async () => {
+      const identifier = 'my-device-id';
+      const mockResponse = {
+        success: true,
+        data: {
+          defaultOptions: [{ code: 'EBBINGHAUS', title: '에빙하우스' }],
+          customOptions: []
+        }
+      };
+      sendMessageMock.mockResolvedValue(mockResponse);
+
+      const result = await getCycleOptions(identifier);
+
+      expect(sendMessageMock).toHaveBeenCalledWith({
+        type: 'API_REQUEST',
+        request: {
+          endpoint: '/api/v1/cycles/custom',
+          method: 'GET',
+          headers: { 'X-Device-Id': identifier }
+        }
+      });
+      expect(result).toEqual(mockResponse.data);
+    });
+  });
+
+  describe('createCustomCycle', () => {
+    it('커스텀 주기를 생성한다', async () => {
+      const identifier = 'my-device-id';
+      const title = '나의 주기';
+      const durations = ['PT10M', 'PT1H', 'P1D'];
+      const mockResponse = { success: true, data: { id: 1, title, durations } };
+      sendMessageMock.mockResolvedValue(mockResponse);
+
+      const result = await createCustomCycle(identifier, title, durations);
+
+      expect(sendMessageMock).toHaveBeenCalledWith({
+        type: 'API_REQUEST',
+        request: {
+          endpoint: '/api/v1/cycles/custom',
+          method: 'POST',
+          headers: { 'X-Device-Id': identifier },
+          body: { title, durations }
+        }
+      });
+      expect(result).toEqual(mockResponse.data);
+    });
+  });
+
+  describe('updateCustomCycle', () => {
+    it('커스텀 주기를 수정한다', async () => {
+      const identifier = 'my-device-id';
+      const id = 1;
+      const title = '수정된 주기';
+      const durations = ['PT30M', 'P2D'];
+      const mockResponse = { success: true, data: { id, title, durations } };
+      sendMessageMock.mockResolvedValue(mockResponse);
+
+      const result = await updateCustomCycle(identifier, id, title, durations);
+
+      expect(sendMessageMock).toHaveBeenCalledWith({
+        type: 'API_REQUEST',
+        request: {
+          endpoint: '/api/v1/cycles/custom/1',
+          method: 'PUT',
+          headers: { 'X-Device-Id': identifier },
+          body: { title, durations }
+        }
+      });
+      expect(result).toEqual(mockResponse.data);
+    });
+  });
+
+  describe('deleteCustomCycle', () => {
+    it('커스텀 주기를 삭제한다', async () => {
+      const identifier = 'my-device-id';
+      const id = 1;
+      const mockResponse = { success: true, data: null };
+      sendMessageMock.mockResolvedValue(mockResponse);
+
+      await deleteCustomCycle(identifier, id);
+
+      expect(sendMessageMock).toHaveBeenCalledWith({
+        type: 'API_REQUEST',
+        request: {
+          endpoint: '/api/v1/cycles/custom/1',
+          method: 'DELETE',
+          headers: { 'X-Device-Id': identifier }
         }
       });
     });
diff --git a/src/api.js b/src/api.js
index 8da19cd..5660700 100644
--- a/src/api.js
+++ b/src/api.js
@@ -78,13 +78,73 @@ export async function deleteDevice(email, deviceIdentifier, targetDeviceIdentifi
  * 복습 URL 저장
  * @param {string} identifier - 디바이스 식별자
  * @param {string} targetUrl - 저장할 URL
+ * @param {Object} cycle - 복습 주기 { type: "DEFAULT", code } 또는 { type: "CUSTOM", id }
  * @returns {Promise<Object>} { url, scheduledAts }
  */
-export async function saveReviewUrl(identifier, targetUrl) {
+export async function saveReviewUrl(identifier, targetUrl, cycle) {
   return await sendApiRequest({
     endpoint: '/api/v1/reviews',
     method: 'POST',
     headers: { 'X-Device-Id': identifier },
-    body: { targetUrl }
+    body: { targetUrl, cycle }
+  });
+}
+
+/**
+ * 복습 주기 옵션 조회
+ * @param {string} identifier - 디바이스 식별자
+ * @returns {Promise<Object>} { defaultOptions, customOptions }
+ */
+export async function getCycleOptions(identifier) {
+  return await sendApiRequest({
+    endpoint: '/api/v1/cycles/custom',
+    method: 'GET',
+    headers: { 'X-Device-Id': identifier }
+  });
+}
+
+/**
+ * 커스텀 주기 생성
+ * @param {string} identifier - 디바이스 식별자
+ * @param {string} title - 주기 이름
+ * @param {string[]} durations - ISO 8601 Duration 배열
+ * @returns {Promise<Object>} { id, title, durations }
+ */
+export async function createCustomCycle(identifier, title, durations) {
+  return await sendApiRequest({
+    endpoint: '/api/v1/cycles/custom',
+    method: 'POST',
+    headers: { 'X-Device-Id': identifier },
+    body: { title, durations }
+  });
+}
+
+/**
+ * 커스텀 주기 수정
+ * @param {string} identifier - 디바이스 식별자
+ * @param {number} id - 주기 ID
+ * @param {string} title - 주기 이름
+ * @param {string[]} durations - ISO 8601 Duration 배열
+ * @returns {Promise<Object>} { id, title, durations }
+ */
+export async function updateCustomCycle(identifier, id, title, durations) {
+  return await sendApiRequest({
+    endpoint: `/api/v1/cycles/custom/${id}`,
+    method: 'PUT',
+    headers: { 'X-Device-Id': identifier },
+    body: { title, durations }
+  });
+}
+
+/**
+ * 커스텀 주기 삭제
+ * @param {string} identifier - 디바이스 식별자
+ * @param {number} id - 주기 ID
+ */
+export async function deleteCustomCycle(identifier, id) {
+  return await sendApiRequest({
+    endpoint: `/api/v1/cycles/custom/${id}`,
+    method: 'DELETE',
+    headers: { 'X-Device-Id': identifier }
   });
 }
diff --git a/src/constants.js b/src/constants.js
index 13a535f..a0626f3 100644
--- a/src/constants.js
+++ b/src/constants.js
@@ -1,7 +1,11 @@
 /**
  * 상수 정의
  *
- * 에러 코드 및 자동 로그아웃이 필요한 에러 목록을 정의한다.
+ * 에러 코드, UI 설정값, Duration 관련 상수를 정의한다.
+ */
+
+/**
+ * 에러 코드
  */
 export const ERROR_CODES = {
   // 로그아웃이 필요한 에러
@@ -23,3 +27,26 @@ export const LOGOUT_REQUIRED_ERRORS = [
   ERROR_CODES.NOT_FOUND,
   ERROR_CODES.INVALID_STORAGE
 ];
+
+/**
+ * UI 관련 상수
+ */
+export const UI_CONSTANTS = {
+  MESSAGE_DISPLAY_DURATION_MS: 3000,      // 메시지 표시 시간 (3초)
+  DEVICE_ID_DISPLAY_LENGTH: 20            // 디바이스 ID 표시 길이
+};
+
+/**
+ * Duration 관련 상수
+ */
+export const DURATION_CONSTANTS = {
+  VALIDATION_STEP_MINUTES: 10,            // 분 단위 검증 기준 (10분)
+  DEFAULT_DURATION: 'PT10M',              // 기본 Duration 값
+  DEFAULT_VALUE: 10,                      // 기본 숫자 값
+  DEFAULT_UNIT: 'M'                       // 기본 단위 (분)
+};
+
+/**
+ * ISO 8601 Duration 파싱용 정규식
+ */
+export const DURATION_REGEX = /^P(?:(\d+)D)?(?:T(?:(\d+)H)?(?:(\d+)M)?)?$/;
diff --git a/src/duration-utils.js b/src/duration-utils.js
new file mode 100644
index 0000000..c22c78d
--- /dev/null
+++ b/src/duration-utils.js
@@ -0,0 +1,102 @@
+/**
+ * Duration 유틸리티
+ *
+ * ISO 8601 Duration 형식의 파싱, 변환, 검증을 담당한다.
+ */
+
+import { DURATION_REGEX, DURATION_CONSTANTS } from './constants.js';
+
+/**
+ * ISO 8601 Duration을 파싱하여 일/시간/분 값 반환
+ * @param {string} duration - ISO 8601 Duration (예: 'P1D', 'PT1H', 'PT10M')
+ * @returns {{ days: number, hours: number, minutes: number }}
+ */
+export function parseDuration(duration) {
+  const match = duration.match(DURATION_REGEX);
+  if (!match) {
+    return { days: 0, hours: 0, minutes: 0 };
+  }
+
+  return {
+    days: parseInt(match[1]) || 0,
+    hours: parseInt(match[2]) || 0,
+    minutes: parseInt(match[3]) || 0
+  };
+}
+
+/**
+ * ISO 8601 Duration을 읽기 쉬운 텍스트로 변환
+ * @param {string} duration - ISO 8601 Duration
+ * @returns {string} 예: '1일', '2시간', '10분', '1일 2시간'
+ */
+export function formatDurationToText(duration) {
+  const { days, hours, minutes } = parseDuration(duration);
+
+  const parts = [];
+  if (days > 0) parts.push(`${days}일`);
+  if (hours > 0) parts.push(`${hours}시간`);
+  if (minutes > 0) parts.push(`${minutes}분`);
+
+  return parts.join(' ') || duration;
+}
+
+/**
+ * Duration 배열을 표시용 문자열로 변환
+ * @param {string[]} durations - ISO 8601 Duration 배열
+ * @returns {string} 예: '10분 → 1시간 → 1일'
+ */
+export function formatDurationsForDisplay(durations) {
+  if (!durations || durations.length === 0) return '';
+  return durations.map(d => formatDurationToText(d)).join(' → ');
+}
+
+/**
+ * ISO 8601 Duration을 값과 단위로 변환 (폼 입력용)
+ * @param {string} duration - ISO 8601 Duration
+ * @returns {{ value: number, unit: string }} unit: 'D' | 'H' | 'M'
+ */
+export function parseDurationToValueUnit(duration) {
+  const { days, hours, minutes } = parseDuration(duration);
+
+  if (days > 0) return { value: days, unit: 'D' };
+  if (hours > 0) return { value: hours, unit: 'H' };
+  return {
+    value: minutes || DURATION_CONSTANTS.DEFAULT_VALUE,
+    unit: DURATION_CONSTANTS.DEFAULT_UNIT
+  };
+}
+
+/**
+ * 값과 단위를 ISO 8601 Duration으로 변환
+ * @param {number} value - 숫자 값
+ * @param {string} unit - 단위 ('D' | 'H' | 'M')
+ * @returns {string} ISO 8601 Duration
+ */
+export function formatValueUnitToDuration(value, unit) {
+  if (unit === 'D') return `P${value}D`;
+  if (unit === 'H') return `PT${value}H`;
+  return `PT${value}M`;
+}
+
+/**
+ * Duration 배열 검증 (10분 단위)
+ * @param {string[]} durations - ISO 8601 Duration 배열
+ * @returns {{ valid: boolean, message: string }}
+ */
+export function validateDurations(durations) {
+  if (durations.length === 0) {
+    return { valid: false, message: '최소 1개의 복습 간격이 필요합니다.' };
+  }
+
+  for (const d of durations) {
+    const match = d.match(/^PT(\d+)M$/);
+    if (match) {
+      const minutes = parseInt(match[1]);
+      if (minutes % DURATION_CONSTANTS.VALIDATION_STEP_MINUTES !== 0) {
+        return { valid: false, message: '분 단위는 10분 단위로 입력해주세요.' };
+      }
+    }
+  }
+
+  return { valid: true, message: '' };
+}
diff --git a/src/handlers/auth.js b/src/handlers/auth.js
new file mode 100644
index 0000000..5034a9d
--- /dev/null
+++ b/src/handlers/auth.js
@@ -0,0 +1,91 @@
+/**
+ * 인증 관련 핸들러
+ *
+ * 디바이스 등록, 인증 확인, 리셋 처리를 담당한다.
+ */
+
+import { STORAGE_KEYS } from '../config.js';
+import { ERROR_CODES } from '../constants.js';
+import { registerDevice, getDevices } from '../api.js';
+import { setStorageData, clearStorage, validateStorageForAuth } from '../storage.js';
+import {
+  elements,
+  showLoading,
+  hideLoading,
+  showMessage,
+  showView,
+  handleApiError
+} from '../ui/index.js';
+import { isValidEmail } from '../utils.js';
+
+/**
+ * 디바이스 등록 버튼 클릭 핸들러
+ */
+export async function handleRegister() {
+  const email = elements.emailInput.value.trim();
+
+  if (!email) {
+    showMessage('이메일을 입력해주세요.', 'error');
+    return;
+  }
+
+  if (!isValidEmail(email)) {
+    showMessage('유효한 이메일 형식이 아닙니다.', 'error');
+    return;
+  }
+
+  try {
+    showLoading();
+    const result = await registerDevice(email);
+
+    await setStorageData({
+      [STORAGE_KEYS.EMAIL]: result.email,
+      [STORAGE_KEYS.IDENTIFIER]: result.identifier,
+      [STORAGE_KEYS.IS_AUTHENTICATED]: false
+    });
+
+    elements.emailDisplay.textContent = result.email;
+    showView('pending');
+    showMessage('이메일로 인증 링크가 전송되었습니다.', 'success');
+  } catch (error) {
+    showMessage(error.message, 'error');
+  } finally {
+    hideLoading();
+  }
+}
+
+/**
+ * 인증 확인 버튼 클릭 핸들러
+ */
+export async function handleCheckAuth() {
+  try {
+    showLoading();
+    const storageData = await validateStorageForAuth();
+    const result = await getDevices(storageData.email, storageData.identifier);
+
+    await setStorageData({
+      [STORAGE_KEYS.IS_AUTHENTICATED]: true
+    });
+
+    elements.userEmail.textContent = result.email;
+    showView('main');
+    showMessage('인증이 완료되었습니다!', 'success');
+  } catch (error) {
+    if (error.code === ERROR_CODES.UNAUTHORIZED) {
+      showMessage('아직 인증이 완료되지 않았습니다.', 'info');
+    } else {
+      await handleApiError(error);
+    }
+  } finally {
+    hideLoading();
+  }
+}
+
+/**
+ * 다른 이메일로 등록 버튼 클릭 핸들러
+ */
+export async function handleReset() {
+  await clearStorage();
+  elements.emailInput.value = '';
+  showView('login');
+}
diff --git a/src/handlers/cycle.js b/src/handlers/cycle.js
new file mode 100644
index 0000000..e415d23
--- /dev/null
+++ b/src/handlers/cycle.js
@@ -0,0 +1,188 @@
+/**
+ * 복습 주기 관련 핸들러
+ *
+ * 주기 옵션 로드, 생성, 수정, 삭제 처리를 담당한다.
+ */
+
+import {
+  getCycleOptions,
+  createCustomCycle,
+  updateCustomCycle,
+  deleteCustomCycle
+} from '../api.js';
+import { validateStorageForAuth } from '../storage.js';
+import {
+  elements,
+  showLoading,
+  hideLoading,
+  showMessage,
+  handleApiError,
+  renderCycleSelect,
+  renderCycleList,
+  showCycleModal,
+  hideCycleModal,
+  getEditingCycleId,
+  addDurationInput,
+  getDurationsFromForm
+} from '../ui/index.js';
+import { validateDurations } from '../duration-utils.js';
+
+// 현재 로드된 주기 옵션 캐시
+let cachedCycleOptions = { defaultOptions: [], customOptions: [] };
+
+/**
+ * 캐시된 주기 옵션 반환
+ * @returns {{ defaultOptions: Array, customOptions: Array }}
+ */
+export function getCachedCycleOptions() {
+  return cachedCycleOptions;
+}
+
+/**
+ * 주기 옵션 로드 핸들러
+ */
+export async function handleLoadCycleOptions() {
+  try {
+    const storageData = await validateStorageForAuth();
+    const result = await getCycleOptions(storageData.identifier);
+
+    cachedCycleOptions = {
+      defaultOptions: result.defaultOptions || [],
+      customOptions: result.customOptions || []
+    };
+
+    renderCycleSelect(cachedCycleOptions.defaultOptions, cachedCycleOptions.customOptions);
+  } catch (error) {
+    console.warn('주기 옵션 로드 실패:', error);
+    // 에러 시에도 기본 빈 상태로 렌더링
+    renderCycleSelect([], []);
+  }
+}
+
+/**
+ * 주기 관리 섹션 토글 핸들러
+ */
+export async function handleShowCycleManagement() {
+  const isVisible = !elements.cycleSection.classList.contains('hidden');
+
+  if (isVisible) {
+    elements.cycleSection.classList.add('hidden');
+    return;
+  }
+
+  try {
+    showLoading();
+    const storageData = await validateStorageForAuth();
+    const result = await getCycleOptions(storageData.identifier);
+
+    cachedCycleOptions = {
+      defaultOptions: result.defaultOptions || [],
+      customOptions: result.customOptions || []
+    };
+
+    renderCycleList(cachedCycleOptions.customOptions);
+    elements.cycleSection.classList.remove('hidden');
+  } catch (error) {
+    await handleApiError(error);
+  } finally {
+    hideLoading();
+  }
+}
+
+/**
+ * 커스텀 주기 저장 핸들러 (생성/수정)
+ * @param {Event} e - 폼 제출 이벤트
+ */
+export async function handleSaveCycle(e) {
+  e.preventDefault();
+
+  const title = elements.cycleTitleInput.value.trim();
+  if (!title) {
+    showMessage('주기 이름을 입력해주세요.', 'error');
+    return;
+  }
+
+  const durations = getDurationsFromForm();
+  const validation = validateDurations(durations);
+  if (!validation.valid) {
+    showMessage(validation.message, 'error');
+    return;
+  }
+
+  try {
+    showLoading();
+    const storageData = await validateStorageForAuth();
+    const editingId = getEditingCycleId();
+
+    if (editingId) {
+      // 수정
+      await updateCustomCycle(storageData.identifier, editingId, title, durations);
+      showMessage('주기가 수정되었습니다.', 'success');
+    } else {
+      // 생성
+      await createCustomCycle(storageData.identifier, title, durations);
+      showMessage('주기가 생성되었습니다.', 'success');
+    }
+
+    hideCycleModal();
+
+    // 목록 및 드롭다운 갱신
+    await handleLoadCycleOptions();
+    renderCycleList(cachedCycleOptions.customOptions);
+  } catch (error) {
+    await handleApiError(error);
+  } finally {
+    hideLoading();
+  }
+}
+
+/**
+ * 커스텀 주기 삭제 핸들러
+ * @param {number} id - 주기 ID
+ */
+export async function handleDeleteCycle(id) {
+  if (!confirm('이 복습 주기를 삭제하시겠습니까?')) {
+    return;
+  }
+
+  try {
+    showLoading();
+    const storageData = await validateStorageForAuth();
+    await deleteCustomCycle(storageData.identifier, id);
+
+    showMessage('주기가 삭제되었습니다.', 'success');
+
+    // 목록 및 드롭다운 갱신
+    await handleLoadCycleOptions();
+    renderCycleList(cachedCycleOptions.customOptions);
+  } catch (error) {
+    await handleApiError(error);
+  } finally {
+    hideLoading();
+  }
+}
+
+/**
+ * 커스텀 주기 수정 모달 열기 핸들러
+ * @param {number} id - 주기 ID
+ */
+export function handleEditCycle(id) {
+  const cycle = cachedCycleOptions.customOptions.find(c => c.id === id);
+  if (cycle) {
+    showCycleModal(cycle);
+  }
+}
+
+/**
+ * 새 주기 추가 버튼 클릭 핸들러
+ */
+export function handleAddCycle() {
+  showCycleModal(null);
+}
+
+/**
+ * Duration 추가 버튼 클릭 핸들러
+ */
+export function handleAddDuration() {
+  addDurationInput();
+}
diff --git a/src/handlers.js b/src/handlers/device.js
similarity index 51%
rename from src/handlers.js
rename to src/handlers/device.js
index 7db7904..fb8c806 100644
--- a/src/handlers.js
+++ b/src/handlers/device.js
@@ -1,14 +1,12 @@
 /**
- * 이벤트 핸들러
+ * 디바이스 관련 핸들러
  *
- * 디바이스 등록, 인증 확인, URL 저장, 디바이스 관리, 로그아웃 등
- * 사용자 액션에 대한 핸들러 함수를 정의한다.
+ * 디바이스 목록 조회, 삭제, 로그아웃 처리를 담당한다.
  */
 
-import { STORAGE_KEYS } from './config.js';
-import { ERROR_CODES } from './constants.js';
-import { registerDevice, getDevices, deleteDevice, saveReviewUrl } from './api.js';
-import { setStorageData, clearStorage, validateStorageForAuth } from './storage.js';
+import { UI_CONSTANTS } from '../constants.js';
+import { getDevices, deleteDevice } from '../api.js';
+import { getStorageData, clearStorage, validateStorageForAuth } from '../storage.js';
 import {
   elements,
   showLoading,
@@ -16,113 +14,8 @@ import {
   showMessage,
   showView,
   handleApiError
-} from './ui.js';
-import { formatDate, isValidEmail } from './utils.js';
-
-/**
- * 디바이스 등록 버튼 클릭 핸들러
- */
-export async function handleRegister() {
-  const email = elements.emailInput.value.trim();
-
-  if (!email) {
-    showMessage('이메일을 입력해주세요.', 'error');
-    return;
-  }
-
-  if (!isValidEmail(email)) {
-    showMessage('유효한 이메일 형식이 아닙니다.', 'error');
-    return;
-  }
-
-  try {
-    showLoading();
-    const result = await registerDevice(email);
-
-    await setStorageData({
-      [STORAGE_KEYS.EMAIL]: result.email,
-      [STORAGE_KEYS.IDENTIFIER]: result.identifier,
-      [STORAGE_KEYS.IS_AUTHENTICATED]: false
-    });
-
-    elements.emailDisplay.textContent = result.email;
-    showView('pending');
-    showMessage('이메일로 인증 링크가 전송되었습니다.', 'success');
-  } catch (error) {
-    showMessage(error.message, 'error');
-  } finally {
-    hideLoading();
-  }
-}
-
-/**
- * 인증 확인 버튼 클릭 핸들러
- */
-export async function handleCheckAuth() {
-  try {
-    showLoading();
-    const storageData = await validateStorageForAuth();
-    const result = await getDevices(storageData.email, storageData.identifier);
-
-    await setStorageData({
-      [STORAGE_KEYS.IS_AUTHENTICATED]: true
-    });
-
-    elements.userEmail.textContent = result.email;
-    showView('main');
-    showMessage('인증이 완료되었습니다!', 'success');
-  } catch (error) {
-    if (error.code === ERROR_CODES.UNAUTHORIZED) {
-      showMessage('아직 인증이 완료되지 않았습니다.', 'info');
-    } else {
-      await handleApiError(error);
-    }
-  } finally {
-    hideLoading();
-  }
-}
-
-/**
- * 다른 이메일로 등록 버튼 클릭 핸들러
- */
-export async function handleReset() {
-  await clearStorage();
-  elements.emailInput.value = '';
-  showView('login');
-}
-
-/**
- * URL 저장 버튼 클릭 핸들러
- */
-export async function handleSaveUrl() {
-  try {
-    showLoading();
-
-    const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
-
-    if (!tab?.url) {
-      showMessage('현재 페이지의 URL을 가져올 수 없습니다.', 'error');
-      return;
-    }
-
-    const storageData = await validateStorageForAuth();
-    const result = await saveReviewUrl(storageData.identifier, tab.url);
-
-    elements.scheduleDates.innerHTML = '';
-    result.scheduledAts.forEach(date => {
-      const li = document.createElement('li');
-      li.textContent = formatDate(date);
-      elements.scheduleDates.appendChild(li);
-    });
-
-    elements.saveResult.classList.remove('hidden');
-    showMessage('저장되었습니다!', 'success');
-  } catch (error) {
-    await handleApiError(error);
-  } finally {
-    hideLoading();
-  }
-}
+} from '../ui/index.js';
+import { formatDate } from '../utils.js';
 
 /**
  * 디바이스 관리 버튼 클릭 핸들러
@@ -151,7 +44,7 @@ export async function handleShowDevices() {
 
       const deviceIdDiv = document.createElement('div');
       deviceIdDiv.className = 'device-id';
-      deviceIdDiv.textContent = device.identifier.substring(0, 20) + '...';
+      deviceIdDiv.textContent = device.identifier.substring(0, UI_CONSTANTS.DEVICE_ID_DISPLAY_LENGTH) + '...';
       deviceInfo.appendChild(deviceIdDiv);
 
       const deviceDateDiv = document.createElement('div');
@@ -227,12 +120,12 @@ export async function handleLogout() {
   try {
     showLoading();
     const storageData = await getStorageData();
-    
+
     // 인증된 상태라면 서버에 디바이스 삭제 요청
     if (storageData.email && storageData.identifier) {
       await deleteDevice(
-        storageData.email, 
-        storageData.identifier, 
+        storageData.email,
+        storageData.identifier,
         storageData.identifier // 자기 자신을 삭제
       );
     }
@@ -245,6 +138,7 @@ export async function handleLogout() {
   await clearStorage();
   elements.saveResult.classList.add('hidden');
   elements.devicesSection.classList.add('hidden');
+  elements.cycleSection.classList.add('hidden');
   showView('login');
   showMessage('로그아웃 되었습니다.', 'info');
 }
diff --git a/src/handlers/index.js b/src/handlers/index.js
new file mode 100644
index 0000000..db65c28
--- /dev/null
+++ b/src/handlers/index.js
@@ -0,0 +1,26 @@
+/**
+ * 핸들러 모듈 진입점
+ *
+ * 모든 핸들러를 re-export한다.
+ */
+
+// 인증 관련
+export { handleRegister, handleCheckAuth, handleReset } from './auth.js';
+
+// 디바이스 관련
+export { handleShowDevices, handleDeleteDevice, handleLogout } from './device.js';
+
+// 주기 관련
+export {
+  handleLoadCycleOptions,
+  handleShowCycleManagement,
+  handleSaveCycle,
+  handleDeleteCycle,
+  handleEditCycle,
+  handleAddCycle,
+  handleAddDuration,
+  getCachedCycleOptions
+} from './cycle.js';
+
+// URL 저장 관련
+export { handleSaveUrl } from './url.js';
diff --git a/src/handlers/url.js b/src/handlers/url.js
new file mode 100644
index 0000000..47c383c
--- /dev/null
+++ b/src/handlers/url.js
@@ -0,0 +1,51 @@
+/**
+ * URL 저장 관련 핸들러
+ *
+ * 현재 페이지 URL 저장 처리를 담당한다.
+ */
+
+import { saveReviewUrl } from '../api.js';
+import { validateStorageForAuth } from '../storage.js';
+import {
+  elements,
+  showLoading,
+  hideLoading,
+  showMessage,
+  handleApiError,
+  getSelectedCycle
+} from '../ui/index.js';
+import { formatDate } from '../utils.js';
+
+/**
+ * URL 저장 버튼 클릭 핸들러
+ */
+export async function handleSaveUrl() {
+  try {
+    showLoading();
+
+    const [tab] = await chrome.tabs.query({ active: true, currentWindow: true });
+
+    if (!tab?.url) {
+      showMessage('현재 페이지의 URL을 가져올 수 없습니다.', 'error');
+      return;
+    }
+
+    const storageData = await validateStorageForAuth();
+    const cycle = getSelectedCycle();
+    const result = await saveReviewUrl(storageData.identifier, tab.url, cycle);
+
+    elements.scheduleDates.innerHTML = '';
+    result.scheduledAts.forEach(date => {
+      const li = document.createElement('li');
+      li.textContent = formatDate(date);
+      elements.scheduleDates.appendChild(li);
+    });
+
+    elements.saveResult.classList.remove('hidden');
+    showMessage('저장되었습니다!', 'success');
+  } catch (error) {
+    await handleApiError(error);
+  } finally {
+    hideLoading();
+  }
+}
diff --git a/src/popup.js b/src/popup.js
index b72c286..bcf4f1c 100644
--- a/src/popup.js
+++ b/src/popup.js
@@ -9,8 +9,9 @@ import {
   elements,
   initializeElements,
   showView,
-  showMessage
-} from './ui.js';
+  showMessage,
+  hideCycleModal
+} from './ui/index.js';
 import {
   handleRegister,
   handleCheckAuth,
@@ -18,8 +19,15 @@ import {
   handleSaveUrl,
   handleShowDevices,
   handleDeleteDevice,
-  handleLogout
-} from './handlers.js';
+  handleLogout,
+  handleLoadCycleOptions,
+  handleShowCycleManagement,
+  handleSaveCycle,
+  handleDeleteCycle,
+  handleEditCycle,
+  handleAddCycle,
+  handleAddDuration
+} from './handlers/index.js';
 
 /**
  * 이벤트 리스너 등록
@@ -32,6 +40,23 @@ function setupEventListeners() {
   elements.showDevicesBtn.addEventListener('click', handleShowDevices);
   elements.logoutBtn.addEventListener('click', handleLogout);
 
+  // 주기 관리 이벤트
+  elements.cycleManageBtn.addEventListener('click', handleShowCycleManagement);
+  elements.cycleAddBtn.addEventListener('click', handleAddCycle);
+  elements.cycleFormCancelBtn.addEventListener('click', hideCycleModal);
+  elements.cycleForm.addEventListener('submit', handleSaveCycle);
+  elements.addDurationBtn.addEventListener('click', handleAddDuration);
+
+  // 주기 목록 이벤트 위임 (수정/삭제)
+  elements.cycleList.addEventListener('click', (e) => {
+    const id = parseInt(e.target.dataset.id, 10);
+    if (e.target.classList.contains('cycle-edit-btn')) {
+      handleEditCycle(id);
+    } else if (e.target.classList.contains('cycle-delete-btn')) {
+      handleDeleteCycle(id);
+    }
+  });
+
   // 디바이스 삭제 버튼 (이벤트 위임)
   elements.devicesList.addEventListener('click', (e) => {
     if (e.target.classList.contains('btn-danger')) {
@@ -67,6 +92,8 @@ async function initialize() {
     if (storageData.isAuthenticated) {
       elements.userEmail.textContent = storageData.email;
       showView('main');
+      // 주기 옵션 로드
+      handleLoadCycleOptions();
     } else if (storageData.email && storageData.identifier) {
       elements.emailDisplay.textContent = storageData.email;
       showView('pending');
diff --git a/src/ui.js b/src/ui.js
deleted file mode 100644
index 481b19e..0000000
--- a/src/ui.js
+++ /dev/null
@@ -1,153 +0,0 @@
-/**
- * UI 관련 함수
- *
- * DOM 요소 캐싱, 로딩/메시지 표시, 뷰 전환, 에러 처리 등
- * 화면 표시와 관련된 기능을 담당한다.
- */
-
-import { clearStorage } from './storage.js';
-import { getErrorMessage, isLogoutRequiredError } from './errors.js';
-import { ERROR_CODES } from './constants.js';
-
-/**
- * DOM 요소 캐시
- */
-export const elements = {
-  // 뷰
-  loginView: null,
-  pendingView: null,
-  mainView: null,
-
-  // 로그인 화면
-  emailInput: null,
-  registerBtn: null,
-
-  // 인증 대기 화면
-  emailDisplay: null,
-  checkAuthBtn: null,
-  resetBtn: null,
-
-  // 메인 화면
-  userEmail: null,
-  saveUrlBtn: null,
-  saveResult: null,
-  scheduleDates: null,
-  showDevicesBtn: null,
-  devicesSection: null,
-  devicesList: null,
-  logoutBtn: null,
-
-  // 공통
-  messageArea: null,
-  loading: null
-};
-
-/**
- * DOM 요소 초기화
- */
-export function initializeElements() {
-  elements.loginView = document.getElementById('login-view');
-  elements.pendingView = document.getElementById('pending-view');
-  elements.mainView = document.getElementById('main-view');
-
-  elements.emailInput = document.getElementById('email-input');
-  elements.registerBtn = document.getElementById('register-btn');
-
-  elements.emailDisplay = document.querySelector('.email-display');
-  elements.checkAuthBtn = document.getElementById('check-auth-btn');
-  elements.resetBtn = document.getElementById('reset-btn');
-
-  elements.userEmail = document.getElementById('user-email');
-  elements.saveUrlBtn = document.getElementById('save-url-btn');
-  elements.saveResult = document.getElementById('save-result');
-  elements.scheduleDates = document.getElementById('schedule-dates');
-  elements.showDevicesBtn = document.getElementById('show-devices-btn');
-  elements.devicesSection = document.getElementById('devices-section');
-  elements.devicesList = document.getElementById('devices-list');
-  elements.logoutBtn = document.getElementById('logout-btn');
-
-  elements.messageArea = document.getElementById('message-area');
-  elements.loading = document.getElementById('loading');
-}
-
-/**
- * 로딩 표시
- */
-export function showLoading() {
-  elements.loading.classList.remove('hidden');
-}
-
-/**
- * 로딩 숨김
- */
-export function hideLoading() {
-  elements.loading.classList.add('hidden');
-}
-
-/**
- * 메시지 표시
- * @param {string} message - 표시할 메시지
- * @param {string} type - 메시지 타입 ('info' | 'success' | 'error')
- */
-export function showMessage(message, type = 'info') {
-  elements.messageArea.textContent = message;
-  elements.messageArea.className = `message-area ${type}`;
-  elements.messageArea.classList.remove('hidden');
-
-  setTimeout(() => {
-    elements.messageArea.classList.add('hidden');
-  }, 3000);
-}
-
-/**
- * 뷰 전환
- * @param {string} viewName - 표시할 뷰 ('login' | 'pending' | 'main')
- */
-export function showView(viewName) {
-  elements.loginView.classList.add('hidden');
-  elements.pendingView.classList.add('hidden');
-  elements.mainView.classList.add('hidden');
-
-  switch (viewName) {
-    case 'login':
-      elements.loginView.classList.remove('hidden');
-      break;
-    case 'pending':
-      elements.pendingView.classList.remove('hidden');
-      break;
-    case 'main':
-      elements.mainView.classList.remove('hidden');
-      break;
-  }
-}
-
-/**
- * 강제 로그아웃 처리
- * @param {string} message - 표시할 메시지
- */
-export async function forceLogout(message) {
-  await clearStorage();
-  elements.saveResult.classList.add('hidden');
-  elements.devicesSection.classList.add('hidden');
-  elements.emailInput.value = '';
-  showView('login');
-  showMessage(message, 'error');
-}
-
-/**
- * 공통 API 에러 핸들러
- * @param {Error} error - 에러 객체
- * @returns {Promise<boolean>} 로그아웃되었으면 true
- */
-export async function handleApiError(error) {
-  const code = error.code || ERROR_CODES.BAD_REQUEST;
-  const message = getErrorMessage(code, error.message);
-
-  if (isLogoutRequiredError(code)) {
-    await forceLogout(message);
-    return true;
-  }
-
-  showMessage(message, 'error');
-  return false;
-}
diff --git a/src/ui/cycle.js b/src/ui/cycle.js
new file mode 100644
index 0000000..f425b10
--- /dev/null
+++ b/src/ui/cycle.js
@@ -0,0 +1,115 @@
+/**
+ * 주기 관련 UI
+ *
+ * 주기 선택 드롭다운 및 주기 목록 렌더링을 담당한다.
+ */
+
+import { elements } from './elements.js';
+import { formatDurationsForDisplay } from '../duration-utils.js';
+
+/**
+ * 주기 선택 드롭다운 렌더링
+ * @param {Array} defaultOptions - 기본 주기 옵션
+ * @param {Array} customOptions - 커스텀 주기 옵션
+ */
+export function renderCycleSelect(defaultOptions, customOptions) {
+  elements.cycleSelect.innerHTML = '';
+
+  // 기본 주기 옵션
+  if (defaultOptions && defaultOptions.length > 0) {
+    const defaultGroup = document.createElement('optgroup');
+    defaultGroup.label = '기본 주기';
+    defaultOptions.forEach(option => {
+      const opt = document.createElement('option');
+      opt.value = `DEFAULT:${option.code}`;
+      opt.textContent = option.title;
+      defaultGroup.appendChild(opt);
+    });
+    elements.cycleSelect.appendChild(defaultGroup);
+  }
+
+  // 커스텀 주기 옵션
+  if (customOptions && customOptions.length > 0) {
+    const customGroup = document.createElement('optgroup');
+    customGroup.label = '나의 주기';
+    customOptions.forEach(option => {
+      const opt = document.createElement('option');
+      opt.value = `CUSTOM:${option.id}`;
+      opt.textContent = option.title;
+      customGroup.appendChild(opt);
+    });
+    elements.cycleSelect.appendChild(customGroup);
+  }
+}
+
+/**
+ * 주기 관리 목록 렌더링
+ * @param {Array} customOptions - 커스텀 주기 옵션
+ */
+export function renderCycleList(customOptions) {
+  elements.cycleList.innerHTML = '';
+
+  if (!customOptions || customOptions.length === 0) {
+    const emptyItem = document.createElement('li');
+    emptyItem.className = 'cycle-item-empty';
+    emptyItem.textContent = '생성된 커스텀 주기가 없습니다.';
+    elements.cycleList.appendChild(emptyItem);
+    return;
+  }
+
+  customOptions.forEach(option => {
+    const li = document.createElement('li');
+    li.className = 'cycle-item';
+    li.setAttribute('data-id', option.id);
+
+    const info = document.createElement('div');
+    info.className = 'cycle-info';
+
+    const title = document.createElement('div');
+    title.className = 'cycle-title';
+    title.textContent = option.title;
+    info.appendChild(title);
+
+    const durations = document.createElement('div');
+    durations.className = 'cycle-durations';
+    durations.textContent = formatDurationsForDisplay(option.durations);
+    info.appendChild(durations);
+
+    li.appendChild(info);
+
+    const actions = document.createElement('div');
+    actions.className = 'cycle-actions';
+
+    const editBtn = document.createElement('button');
+    editBtn.className = 'btn btn-secondary btn-small cycle-edit-btn';
+    editBtn.setAttribute('data-id', option.id);
+    editBtn.textContent = '수정';
+    actions.appendChild(editBtn);
+
+    const deleteBtn = document.createElement('button');
+    deleteBtn.className = 'btn btn-danger btn-small cycle-delete-btn';
+    deleteBtn.setAttribute('data-id', option.id);
+    deleteBtn.textContent = '삭제';
+    actions.appendChild(deleteBtn);
+
+    li.appendChild(actions);
+    elements.cycleList.appendChild(li);
+  });
+}
+
+/**
+ * 선택된 주기 정보 반환
+ * @returns {Object|null} { type, code } 또는 { type, id } 또는 null
+ */
+export function getSelectedCycle() {
+  const value = elements.cycleSelect.value;
+  if (!value) return null;
+
+  const [type, identifier] = value.split(':');
+  if (type === 'DEFAULT') {
+    return { type: 'DEFAULT', code: identifier };
+  } else if (type === 'CUSTOM') {
+    return { type: 'CUSTOM', id: parseInt(identifier, 10) };
+  }
+  return null;
+}
diff --git a/src/ui/elements.js b/src/ui/elements.js
new file mode 100644
index 0000000..8badbfe
--- /dev/null
+++ b/src/ui/elements.js
@@ -0,0 +1,95 @@
+/**
+ * DOM 요소 관리
+ *
+ * DOM 요소 캐싱 및 초기화를 담당한다.
+ */
+
+/**
+ * DOM 요소 캐시
+ */
+export const elements = {
+  // 뷰
+  loginView: null,
+  pendingView: null,
+  mainView: null,
+
+  // 로그인 화면
+  emailInput: null,
+  registerBtn: null,
+
+  // 인증 대기 화면
+  emailDisplay: null,
+  checkAuthBtn: null,
+  resetBtn: null,
+
+  // 메인 화면
+  userEmail: null,
+  cycleSelect: null,
+  saveUrlBtn: null,
+  saveResult: null,
+  scheduleDates: null,
+  cycleManageBtn: null,
+  cycleSection: null,
+  cycleList: null,
+  cycleAddBtn: null,
+  showDevicesBtn: null,
+  devicesSection: null,
+  devicesList: null,
+  logoutBtn: null,
+
+  // 주기 폼 모달
+  cycleModal: null,
+  cycleModalTitle: null,
+  cycleForm: null,
+  cycleTitleInput: null,
+  cycleDurationsContainer: null,
+  addDurationBtn: null,
+  cycleFormSubmitBtn: null,
+  cycleFormCancelBtn: null,
+
+  // 공통
+  messageArea: null,
+  loading: null
+};
+
+/**
+ * DOM 요소 초기화
+ */
+export function initializeElements() {
+  elements.loginView = document.getElementById('login-view');
+  elements.pendingView = document.getElementById('pending-view');
+  elements.mainView = document.getElementById('main-view');
+
+  elements.emailInput = document.getElementById('email-input');
+  elements.registerBtn = document.getElementById('register-btn');
+
+  elements.emailDisplay = document.querySelector('.email-display');
+  elements.checkAuthBtn = document.getElementById('check-auth-btn');
+  elements.resetBtn = document.getElementById('reset-btn');
+
+  elements.userEmail = document.getElementById('user-email');
+  elements.cycleSelect = document.getElementById('cycle-select');
+  elements.saveUrlBtn = document.getElementById('save-url-btn');
+  elements.saveResult = document.getElementById('save-result');
+  elements.scheduleDates = document.getElementById('schedule-dates');
+  elements.cycleManageBtn = document.getElementById('cycle-manage-btn');
+  elements.cycleSection = document.getElementById('cycle-section');
+  elements.cycleList = document.getElementById('cycle-list');
+  elements.cycleAddBtn = document.getElementById('cycle-add-btn');
+  elements.showDevicesBtn = document.getElementById('show-devices-btn');
+  elements.devicesSection = document.getElementById('devices-section');
+  elements.devicesList = document.getElementById('devices-list');
+  elements.logoutBtn = document.getElementById('logout-btn');
+
+  elements.cycleModal = document.getElementById('cycle-modal');
+  elements.cycleModalTitle = document.getElementById('cycle-modal-title');
+  elements.cycleForm = document.getElementById('cycle-form');
+  elements.cycleTitleInput = document.getElementById('cycle-title-input');
+  elements.cycleDurationsContainer = document.getElementById('cycle-durations-container');
+  elements.addDurationBtn = document.getElementById('add-duration-btn');
+  elements.cycleFormSubmitBtn = document.getElementById('cycle-form-submit');
+  elements.cycleFormCancelBtn = document.getElementById('cycle-form-cancel');
+
+  elements.messageArea = document.getElementById('message-area');
+  elements.loading = document.getElementById('loading');
+}
diff --git a/src/ui/error-handler.js b/src/ui/error-handler.js
new file mode 100644
index 0000000..583bd1a
--- /dev/null
+++ b/src/ui/error-handler.js
@@ -0,0 +1,28 @@
+/**
+ * API 에러 처리
+ *
+ * API 에러 처리 및 자동 로그아웃 판단을 담당한다.
+ */
+
+import { ERROR_CODES } from '../constants.js';
+import { getErrorMessage, isLogoutRequiredError } from '../errors.js';
+import { showMessage } from './messages.js';
+import { forceLogout } from './views.js';
+
+/**
+ * 공통 API 에러 핸들러
+ * @param {Error} error - 에러 객체
+ * @returns {Promise<boolean>} 로그아웃되었으면 true
+ */
+export async function handleApiError(error) {
+  const code = error.code || ERROR_CODES.BAD_REQUEST;
+  const message = getErrorMessage(code, error.message);
+
+  if (isLogoutRequiredError(code)) {
+    await forceLogout(message);
+    return true;
+  }
+
+  showMessage(message, 'error');
+  return false;
+}
diff --git a/src/ui/index.js b/src/ui/index.js
new file mode 100644
index 0000000..2c2114e
--- /dev/null
+++ b/src/ui/index.js
@@ -0,0 +1,29 @@
+/**
+ * UI 모듈 진입점
+ *
+ * 모든 UI 함수를 re-export한다.
+ */
+
+// DOM 요소
+export { elements, initializeElements } from './elements.js';
+
+// 뷰 전환
+export { showView, forceLogout } from './views.js';
+
+// 메시지/로딩
+export { showLoading, hideLoading, showMessage } from './messages.js';
+
+// 에러 처리
+export { handleApiError } from './error-handler.js';
+
+// 주기 UI
+export { renderCycleSelect, renderCycleList, getSelectedCycle } from './cycle.js';
+
+// 모달
+export {
+  showCycleModal,
+  hideCycleModal,
+  getEditingCycleId,
+  addDurationInput,
+  getDurationsFromForm
+} from './modal.js';
diff --git a/src/ui/messages.js b/src/ui/messages.js
new file mode 100644
index 0000000..169c63b
--- /dev/null
+++ b/src/ui/messages.js
@@ -0,0 +1,37 @@
+/**
+ * 메시지 및 로딩 표시
+ *
+ * 사용자 피드백 메시지와 로딩 상태 표시를 담당한다.
+ */
+
+import { elements } from './elements.js';
+import { UI_CONSTANTS } from '../constants.js';
+
+/**
+ * 로딩 표시
+ */
+export function showLoading() {
+  elements.loading.classList.remove('hidden');
+}
+
+/**
+ * 로딩 숨김
+ */
+export function hideLoading() {
+  elements.loading.classList.add('hidden');
+}
+
+/**
+ * 메시지 표시
+ * @param {string} message - 표시할 메시지
+ * @param {string} type - 메시지 타입 ('info' | 'success' | 'error')
+ */
+export function showMessage(message, type = 'info') {
+  elements.messageArea.textContent = message;
+  elements.messageArea.className = `message-area ${type}`;
+  elements.messageArea.classList.remove('hidden');
+
+  setTimeout(() => {
+    elements.messageArea.classList.add('hidden');
+  }, UI_CONSTANTS.MESSAGE_DISPLAY_DURATION_MS);
+}
diff --git a/src/ui/modal.js b/src/ui/modal.js
new file mode 100644
index 0000000..e21d8b2
--- /dev/null
+++ b/src/ui/modal.js
@@ -0,0 +1,120 @@
+/**
+ * 모달 관리
+ *
+ * 주기 폼 모달 및 Duration 입력 필드 관리를 담당한다.
+ */
+
+import { elements } from './elements.js';
+import {
+  parseDurationToValueUnit,
+  formatValueUnitToDuration
+} from '../duration-utils.js';
+import { DURATION_CONSTANTS } from '../constants.js';
+
+// 현재 편집 중인 주기 ID (null이면 생성 모드)
+let editingCycleId = null;
+let editingCycleData = null;
+
+/**
+ * 주기 폼 모달 표시
+ * @param {Object|null} cycle - 수정할 주기 (null이면 생성 모드)
+ */
+export function showCycleModal(cycle = null) {
+  editingCycleId = cycle ? cycle.id : null;
+  editingCycleData = cycle;
+
+  elements.cycleModalTitle.textContent = cycle ? '복습 주기 수정' : '새 복습 주기';
+  elements.cycleTitleInput.value = cycle ? cycle.title : '';
+  elements.cycleDurationsContainer.innerHTML = '';
+
+  if (cycle && cycle.durations && cycle.durations.length > 0) {
+    cycle.durations.forEach(d => {
+      addDurationInput(d);
+    });
+  } else {
+    // 기본 하나 추가
+    addDurationInput();
+  }
+
+  elements.cycleModal.classList.remove('hidden');
+}
+
+/**
+ * 주기 폼 모달 숨김
+ */
+export function hideCycleModal() {
+  editingCycleId = null;
+  editingCycleData = null;
+  elements.cycleModal.classList.add('hidden');
+  elements.cycleTitleInput.value = '';
+  elements.cycleDurationsContainer.innerHTML = '';
+}
+
+/**
+ * 현재 편집 중인 주기 ID 반환
+ * @returns {number|null}
+ */
+export function getEditingCycleId() {
+  return editingCycleId;
+}
+
+/**
+ * Duration 입력 필드 추가
+ * @param {string} duration - ISO 8601 Duration (기본: 'PT10M')
+ */
+export function addDurationInput(duration = '') {
+  const group = document.createElement('div');
+  group.className = 'duration-input-group';
+
+  const { value, unit } = parseDurationToValueUnit(
+    duration || DURATION_CONSTANTS.DEFAULT_DURATION
+  );
+
+  const valueInput = document.createElement('input');
+  valueInput.type = 'number';
+  valueInput.min = '1';
+  valueInput.className = 'duration-value';
+  valueInput.value = value;
+
+  const unitSelect = document.createElement('select');
+  unitSelect.className = 'duration-unit';
+  unitSelect.innerHTML = `
+    <option value="M" ${unit === 'M' ? 'selected' : ''}>분</option>
+    <option value="H" ${unit === 'H' ? 'selected' : ''}>시간</option>
+    <option value="D" ${unit === 'D' ? 'selected' : ''}>일</option>
+  `;
+
+  const removeBtn = document.createElement('button');
+  removeBtn.type = 'button';
+  removeBtn.className = 'btn-remove-duration';
+  removeBtn.textContent = '×';
+  removeBtn.addEventListener('click', () => {
+    group.remove();
+  });
+
+  group.appendChild(valueInput);
+  group.appendChild(unitSelect);
+  group.appendChild(removeBtn);
+
+  elements.cycleDurationsContainer.appendChild(group);
+}
+
+/**
+ * 폼에서 durations 배열 추출
+ * @returns {string[]} ISO 8601 Duration 배열
+ */
+export function getDurationsFromForm() {
+  const groups = elements.cycleDurationsContainer.querySelectorAll('.duration-input-group');
+  const durations = [];
+
+  groups.forEach(group => {
+    const value = parseInt(group.querySelector('.duration-value').value) || 0;
+    const unit = group.querySelector('.duration-unit').value;
+
+    if (value > 0) {
+      durations.push(formatValueUnitToDuration(value, unit));
+    }
+  });
+
+  return durations;
+}
diff --git a/src/ui/views.js b/src/ui/views.js
new file mode 100644
index 0000000..b3e3f09
--- /dev/null
+++ b/src/ui/views.js
@@ -0,0 +1,52 @@
+/**
+ * 뷰 전환 관리
+ *
+ * 화면 전환 및 강제 로그아웃 처리를 담당한다.
+ */
+
+import { elements } from './elements.js';
+import { UI_CONSTANTS } from '../constants.js';
+import { clearStorage } from '../storage.js';
+
+/**
+ * 뷰 전환
+ * @param {string} viewName - 표시할 뷰 ('login' | 'pending' | 'main')
+ */
+export function showView(viewName) {
+  elements.loginView.classList.add('hidden');
+  elements.pendingView.classList.add('hidden');
+  elements.mainView.classList.add('hidden');
+
+  switch (viewName) {
+    case 'login':
+      elements.loginView.classList.remove('hidden');
+      break;
+    case 'pending':
+      elements.pendingView.classList.remove('hidden');
+      break;
+    case 'main':
+      elements.mainView.classList.remove('hidden');
+      break;
+  }
+}
+
+/**
+ * 강제 로그아웃 처리
+ * @param {string} message - 표시할 메시지
+ */
+export async function forceLogout(message) {
+  await clearStorage();
+  elements.saveResult.classList.add('hidden');
+  elements.devicesSection.classList.add('hidden');
+  elements.emailInput.value = '';
+  showView('login');
+
+  // 메시지 표시 (순환 참조 방지를 위해 직접 처리)
+  elements.messageArea.textContent = message;
+  elements.messageArea.className = 'message-area error';
+  elements.messageArea.classList.remove('hidden');
+
+  setTimeout(() => {
+    elements.messageArea.classList.add('hidden');
+  }, UI_CONSTANTS.MESSAGE_DISPLAY_DURATION_MS);
+}