diff --git a/README.md b/README.md
index 71915a8..73fe725 100644
--- a/README.md
+++ b/README.md
@@ -40,3 +40,75 @@ python PHJ2000/최빈값.py
 ## 라이선스
 이 프로젝트는 MIT 라이선스를 따릅니다.
 
+<details>
+<summary>📌 전체 Use-Case 다이어그램 (클릭해서 펼치기)</summary>
+%% BRAINNET - Use-Case Diagram
+%% --------------------------------------------------
+%%  Actors
+actor Guest
+actor User
+actor "AI Service" as AI
+actor "Email Service" as Mail
+
+%%  1. Auth
+rectangle "Auth" {
+  Guest -- (Register)
+  Guest -- (Login)
+  User  -- (Logout)
+}
+
+%%  2. 계정 정보
+rectangle "Account" {
+  User -- (View Profile)          : GET /users/me
+  User -- (View Tag Summaries)    : GET /users/me/tag-summaries
+}
+
+%%  3. Project 흐름
+rectangle "Project" {
+  User -- (List Projects)         : GET /projects
+  User -- (Create Project)        : POST /projects
+  User -- (Get Project)           : GET /projects/{id}
+  User -- (Update Project)        : PUT·PATCH /projects/{id}
+  User -- (Delete Project)        : DELETE /projects/{id}
+  User -- (Invite User to Project): POST /projects/{id}/invite
+  User -- (Join Project)          : POST /projects/join
+  User -- (View Project Summary)  : GET /projects/{id}/summary
+}
+
+%%  4. Node 관리
+rectangle "Node" {
+  User -- (List Nodes)            : GET /projects/{id}/nodes
+  User -- (Create Nodes)          : POST /projects/{id}/nodes
+  User -- (Update Node)           : PATCH /projects/{id}/nodes/{nid}
+  User -- (Delete Node)           : DELETE /projects/{id}/nodes/{nid}
+  User -- (Activate Node)         : POST /projects/{id}/nodes/{nid}/activate
+  User -- (Deactivate Node)       : POST /projects/{id}/nodes/{nid}/deactivate
+  (Create Nodes) ..> AI : "GPT-3.5 Turbo\n연관 아이디어"
+}
+
+%%  5. Tag 관리
+rectangle "Tag" {
+  User -- (List Tags)             : GET /projects/{id}/tags
+  User -- (Create Tag)            : POST /projects/{id}/tags
+  User -- (Get Tag)               : GET /projects/{id}/tags/{tid}
+  User -- (Update Tag)            : PATCH /projects/{id}/tags/{tid}
+  User -- (Delete Tag)            : DELETE /projects/{id}/tags/{tid}
+  User -- (Attach Tag to Node)    : POST /projects/{id}/tags/{tid}/nodes/{nid}
+  User -- (Detach Tag from Node)  : DELETE /projects/{id}/tags/{tid}/nodes/{nid}
+}
+
+%%  6. 투표
+rectangle "Vote" {
+  User -- (Cast Vote)             : POST /projects/{id}/tags/{tid}/vote
+  User -- (Confirm Votes)         : POST /projects/{id}/votes/confirm
+}
+
+%%  7. 히스토리
+rectangle "History" {
+  User -- (List History)          : GET /projects/{id}/history
+  User -- (Get History Entry)     : GET /projects/{id}/history/{eid}
+}
+
+%%  외부 서비스 연결
+(Invite User to Project) ..> Mail : "초대 이메일 발송"
+</details>