diff --git a/README.md b/README.md
index 395edc5..82642b2 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,3 @@
 # backend-study-sns
+
+강준이
diff --git a/build.gradle b/build.gradle
index 610d6a6..de1cb7a 100644
--- a/build.gradle
+++ b/build.gradle
@@ -10,7 +10,7 @@ description = 'Demo project for Spring Boot'
 
 java {
 	toolchain {
-		languageVersion = JavaLanguageVersion.of(21)
+		languageVersion = JavaLanguageVersion.of(17)
 	}
 }
 
@@ -19,8 +19,16 @@ repositories {
 }
 
 dependencies {
+    // Lombok
+    compileOnly 'org.projectlombok:lombok'
+    annotationProcessor 'org.projectlombok:lombok'
+
 	implementation 'org.springframework.boot:spring-boot-starter-web'
-	testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
+    implementation 'org.springframework.boot:spring-boot-starter-jdbc'
+    implementation 'org.springframework.boot:spring-boot-starter-thymeleaf'
+    implementation 'com.mysql:mysql-connector-j:8.2.0' // MySQL
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
 	testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
 }
 
diff --git a/src/main/java/com/example/devSns/DevSnsApplication.java b/src/main/java/com/example/devSns/DevSnsApplication.java
index b965724..f1bf185 100644
--- a/src/main/java/com/example/devSns/DevSnsApplication.java
+++ b/src/main/java/com/example/devSns/DevSnsApplication.java
@@ -10,4 +10,4 @@ public static void main(String[] args) {
 		SpringApplication.run(DevSnsApplication.class, args);
 	}
 
-}
+}
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/config/DataInit.java b/src/main/java/com/example/devSns/config/DataInit.java
new file mode 100644
index 0000000..80df5fa
--- /dev/null
+++ b/src/main/java/com/example/devSns/config/DataInit.java
@@ -0,0 +1,24 @@
+package com.example.devSns.config;
+
+import com.example.devSns.entity.MemberEntity;
+import com.example.devSns.repository.MemberRepository;
+import jakarta.annotation.PostConstruct;
+import org.springframework.stereotype.Component;
+
+@Component
+public class DataInit {
+
+    private final MemberRepository memberRepository;
+
+    public DataInit(MemberRepository memberRepository) {
+        this.memberRepository = memberRepository;
+    }
+
+    @PostConstruct
+    public void init() {
+        // Member가 없으면 테스트용 계정 자동 생성
+        if (memberRepository.count() == 0) {
+            memberRepository.save(MemberEntity.create("tester", "tester@example.com"));
+        }
+    }
+}
diff --git a/src/main/java/com/example/devSns/controller/CommentController.java b/src/main/java/com/example/devSns/controller/CommentController.java
new file mode 100644
index 0000000..66874de
--- /dev/null
+++ b/src/main/java/com/example/devSns/controller/CommentController.java
@@ -0,0 +1,31 @@
+package com.example.devSns.controller;
+
+import com.example.devSns.dto.CommentRequest;
+import com.example.devSns.entity.CommentEntity;
+import com.example.devSns.service.CommentService;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.*;
+
+@Controller
+@RequestMapping("/comments")
+public class CommentController {
+    private final CommentService commentService;
+
+    public CommentController(CommentService commentService) {
+        this.commentService = commentService;
+    }
+
+    // 댓글 생성
+    @PostMapping("/{postId}")
+    public String createComment(@PathVariable Long postId, @ModelAttribute CommentRequest request) {
+        commentService.createComment(postId, request);
+        return "redirect:/posts/" + postId;
+    }
+
+    // 댓글 삭제
+    @PostMapping("/{commentId}/delete")
+    public String deleteComment(@PathVariable Long commentId, @RequestParam Long postId) {
+        commentService.deleteComment(commentId);
+        return "redirect:/posts/" + postId;
+    }
+}
diff --git a/src/main/java/com/example/devSns/controller/MemberController.java b/src/main/java/com/example/devSns/controller/MemberController.java
new file mode 100644
index 0000000..1547cb7
--- /dev/null
+++ b/src/main/java/com/example/devSns/controller/MemberController.java
@@ -0,0 +1,61 @@
+package com.example.devSns.controller;
+
+import com.example.devSns.entity.MemberEntity;
+import com.example.devSns.service.MemberService;
+import org.springframework.stereotype.Controller;
+import org.springframework.ui.Model;
+import org.springframework.web.bind.annotation.*;
+
+@Controller
+@RequestMapping("/members")
+public class MemberController {
+
+    private final MemberService memberService;
+
+    public MemberController(MemberService memberService) {
+        this.memberService = memberService;
+    }
+
+     // 전체 멤버 목록
+    @GetMapping
+    public String list(Model model) {
+        model.addAttribute("members", memberService.getAllMembers());
+        return "member-list";
+    }
+
+    // 멤버 상세 페이지
+    @GetMapping("/{id}")
+    public String detail(@PathVariable Long id, Model model) {
+        MemberEntity member = memberService.getMember(id);
+
+        model.addAttribute("member", member);
+        model.addAttribute("posts", member.getPosts());
+        model.addAttribute("comments", member.getComments());
+
+        return "member-detail";
+    }
+
+     // 멤버 생성
+    @GetMapping("/new")
+    public String newForm() {
+        return "member-form";
+    }
+
+    // 멤버 생성 처리
+    @PostMapping
+    public String create(@RequestParam String username,
+                         @RequestParam String email) {
+
+        memberService.createMember(username, email);
+        return "redirect:/members";
+    }
+
+     // 멤버 검색
+     // /members/search?keyword=abc
+    @GetMapping("/search")
+    public String search(@RequestParam String keyword, Model model) {
+        model.addAttribute("members", memberService.search(keyword));
+        model.addAttribute("keyword", keyword);
+        return "member-search";
+    }
+}
diff --git a/src/main/java/com/example/devSns/controller/PostController.java b/src/main/java/com/example/devSns/controller/PostController.java
new file mode 100644
index 0000000..230a3da
--- /dev/null
+++ b/src/main/java/com/example/devSns/controller/PostController.java
@@ -0,0 +1,95 @@
+package com.example.devSns.controller;
+
+import com.example.devSns.entity.MemberEntity;
+import com.example.devSns.entity.PostEntity;
+import com.example.devSns.repository.LikeRepository;
+import com.example.devSns.repository.MemberRepository;
+import com.example.devSns.service.PostService;
+import org.springframework.stereotype.Controller;
+import org.springframework.ui.Model;
+import org.springframework.web.bind.annotation.*;
+
+@Controller
+@RequestMapping("/posts")
+public class PostController {
+
+    private final PostService postService;
+    private final LikeRepository likeRepository;
+    private final MemberRepository memberRepository;
+
+    // 생성자
+    public PostController(PostService postService,
+                          LikeRepository likeRepository,
+                          MemberRepository memberRepository) {
+        this.postService = postService;
+        this.likeRepository = likeRepository;
+        this.memberRepository = memberRepository;
+    }
+
+    // HTTP GET /posts
+    @GetMapping
+    public String list(Model model) {
+        model.addAttribute("posts", postService.getAllPosts());
+        return "list";
+    }
+
+    // HTTP GET /posts/new
+    @GetMapping("/new")
+    public String form(Model model) {
+        model.addAttribute("post", new PostEntity());
+        return "form";
+    }
+
+    // HTTP POST /posts
+    @PostMapping
+    public String create(@ModelAttribute PostEntity postEntity) {
+        postService.createPost(postEntity);
+        return "redirect:/posts"; // 글 생성 후 돌아올 주소
+    }
+
+    // HTTP GET /posts/{id}
+    @GetMapping("/{id}")
+    public String detail(@PathVariable Long id, Model model) {
+        PostEntity postEntity = postService.getPost(id);
+
+        // 임시 멤버 아이디
+        Long memberId = 1L;
+        MemberEntity member = memberRepository.findById(memberId).orElseThrow();
+
+        // 좋아요 수
+        int likeCount = likeRepository.countByPostId(id);
+
+        // 좋아요 여부
+        boolean liked = likeRepository
+                .findByMemberAndPost(member, postEntity)
+                .isPresent();
+
+        model.addAttribute("post", postEntity);
+        model.addAttribute("likeCount", likeCount);
+        model.addAttribute("liked", liked);
+        model.addAttribute("memberId", memberId);
+        return "detail";
+    }
+
+    // HTTP GET /posts/{id}/edit
+    @GetMapping("/{id}/edit")
+    public String editForm(@PathVariable Long id, Model model) {
+        PostEntity postEntity = postService.getPost(id);
+        model.addAttribute("post", postEntity);
+        return "edit";
+    }
+
+    // HTTP POST /posts/{id}/update
+    @PostMapping("/{id}/update")
+    public String update(@PathVariable Long id, @ModelAttribute PostEntity updatedPost) {
+        postService.updatePost(id, updatedPost);
+        return "redirect:/posts/" + id; // 수정 후 돌아올 주소
+    }
+
+    // HTTP POST /posts/{id}/delete
+    @PostMapping("/{id}/delete")
+    public String delete(@PathVariable Long id) {
+        postService.deletePost(id);
+        return "redirect:/posts"; // 삭제 후 돌아올 주소
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/controller/explanation b/src/main/java/com/example/devSns/controller/explanation
new file mode 100644
index 0000000..d86130e
--- /dev/null
+++ b/src/main/java/com/example/devSns/controller/explanation
@@ -0,0 +1,24 @@
+요청을 받는 곳
+
+PostController
+Spring MVC 패턴에서 Controller 계층 역할
+- 사용자의 요청을 받고 Service 계층을 호출해서 처리한 후, 결과를 View에 전달
+
+@Controller
+이 클래스는 웹 요청을 처리하는 컨트롤러임을 알려줌
+- Model에 데이터를 담아 템플릿에 전달 (templates/list.html)
+
+@RequestMapping
+클래스 전체의 기본 URL 경로를 지정
+- 이 컨트롤러 안의 모든 요청은 /posts로 시작
+- /posts (게시글 목록), /posts/new (새 글 작성 폼)
+
+@GetMapping, @PostMapping
+HTTP 메서드 별 라우팅
+
+@PathVariable, @ModelAttribute
+URL 경로 변수 바인딩 / 폼 데이터를 객체에 바인딩
+
+@RestController
+문자열 반환이 뷰 이름이 아닌 JSON
+- REST API 만들 때 사용
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/dto/CommentRequest.java b/src/main/java/com/example/devSns/dto/CommentRequest.java
new file mode 100644
index 0000000..93829ab
--- /dev/null
+++ b/src/main/java/com/example/devSns/dto/CommentRequest.java
@@ -0,0 +1,13 @@
+package com.example.devSns.dto;
+
+import lombok.Getter;
+import lombok.Setter;
+
+@Getter
+@Setter
+public class CommentRequest {
+    private String username;
+    private String content;
+}
+
+// Controller는 CommentEntity를 직접 받지 않고 CommentRequest만 받게 됨
diff --git a/src/main/java/com/example/devSns/dto/CommentResponse.java b/src/main/java/com/example/devSns/dto/CommentResponse.java
new file mode 100644
index 0000000..917576b
--- /dev/null
+++ b/src/main/java/com/example/devSns/dto/CommentResponse.java
@@ -0,0 +1,20 @@
+package com.example.devSns.dto;
+
+import lombok.Getter;
+
+@Getter
+public class CommentResponse {
+    private final Long id;
+    private final String username;
+    private final String content;
+    private final String createdAt;
+
+    public CommentResponse(Long id, String username, String content, String createdAt) {
+        this.id = id;
+        this.username = username;
+        this.content = content;
+        this.createdAt = createdAt;
+    }
+}
+
+// Entity를 외부로 그대로 내보내지 않고 DTO로 가공해서 반환
diff --git a/src/main/java/com/example/devSns/dto/explanation b/src/main/java/com/example/devSns/dto/explanation
new file mode 100644
index 0000000..095c837
--- /dev/null
+++ b/src/main/java/com/example/devSns/dto/explanation
@@ -0,0 +1,8 @@
+계층간 데이터 교환에 사용
+- Entity 클래스를 보호
+- 필요한 데이터만 선택적으로 담을 수 있음
+
+분리해서 사용하는 이유
+- Entity 객체의 변경을 피하기 위함
+- 클라이언트와 통신하는 ResponseDTO나 RequestDTO는 요구사항에 따라 자주 변경
+- 어떤 요청에서는 특정 값이 추가되거나 없을 수 있어서 분리해서 관리
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/entity/CommentEntity.java b/src/main/java/com/example/devSns/entity/CommentEntity.java
new file mode 100644
index 0000000..c263fb9
--- /dev/null
+++ b/src/main/java/com/example/devSns/entity/CommentEntity.java
@@ -0,0 +1,57 @@
+package com.example.devSns.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+
+import java.time.LocalDateTime;
+
+// DTO를 사용하고 Setter를 삭제 (안전)
+@Entity
+@Getter
+public class CommentEntity {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String content;
+    private String username;
+
+    private LocalDateTime createdAt;
+    private LocalDateTime updatedAt;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "member_id")
+    private MemberEntity member;
+
+    // Post와 N:1 관계
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "post_id")
+    private PostEntity postEntity;
+
+    // JPA 기본 생성자
+    protected CommentEntity() {}
+
+    // 정적 생성 메서드 > 엔터티 변경은 오직 메서드로
+    public static CommentEntity create(PostEntity postEntity, String username, String content) {
+        CommentEntity comment = new CommentEntity();
+        comment.postEntity = postEntity;
+        comment.username = username;
+        comment.content = content;
+        return comment;
+    }
+
+    public void updateContent(String content) {
+        this.content = content;
+    }
+
+    @PrePersist
+    public void onCreate() {
+        this.createdAt = LocalDateTime.now();
+        this.updatedAt = LocalDateTime.now();
+    }
+
+    @PreUpdate
+    public void onUpdate() {
+        this.updatedAt = LocalDateTime.now();
+    }
+}
diff --git a/src/main/java/com/example/devSns/entity/LikeEntity.java b/src/main/java/com/example/devSns/entity/LikeEntity.java
new file mode 100644
index 0000000..76218e8
--- /dev/null
+++ b/src/main/java/com/example/devSns/entity/LikeEntity.java
@@ -0,0 +1,33 @@
+package com.example.devSns.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+
+@Entity
+@Getter
+public class LikeEntity {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "member_id")
+    private MemberEntity member;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "post_id")
+    private PostEntity post;
+
+    protected LikeEntity() {}
+
+    public static LikeEntity create(MemberEntity member, PostEntity postEntity) {
+        LikeEntity like = new LikeEntity();
+        like.member = member;
+        like.post = postEntity;
+
+        // JPA 양방향 편의 메서드 -> 자동 갱신
+        member.getLikes().add(like);
+        postEntity.getLikes().add(like);
+        return like;
+    }
+}
diff --git a/src/main/java/com/example/devSns/entity/MemberEntity.java b/src/main/java/com/example/devSns/entity/MemberEntity.java
new file mode 100644
index 0000000..bccb35d
--- /dev/null
+++ b/src/main/java/com/example/devSns/entity/MemberEntity.java
@@ -0,0 +1,40 @@
+package com.example.devSns.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+
+@Entity
+@Getter
+public class MemberEntity {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String username;
+    private String email;
+
+    private LocalDateTime createdAt;
+
+    @OneToMany(mappedBy = "member")
+    private List<PostEntity> posts = new ArrayList<>();
+
+    @OneToMany(mappedBy = "member")
+    private List<CommentEntity> comments = new ArrayList<>();
+
+    @OneToMany(mappedBy = "member")
+    private List<LikeEntity> likes = new ArrayList<>();
+
+    protected MemberEntity() {}
+
+    public static MemberEntity create(String username, String email) {
+        MemberEntity member = new MemberEntity();
+        member.username = username;
+        member.email = email;
+        member.createdAt = LocalDateTime.now();
+        return member;
+    }
+}
diff --git a/src/main/java/com/example/devSns/entity/PostEntity.java b/src/main/java/com/example/devSns/entity/PostEntity.java
new file mode 100644
index 0000000..70b8004
--- /dev/null
+++ b/src/main/java/com/example/devSns/entity/PostEntity.java
@@ -0,0 +1,48 @@
+package com.example.devSns.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.Setter;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+
+@Entity
+@Getter
+@Setter
+public class PostEntity {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String title;
+    private String content;
+    private String author;
+
+    private LocalDateTime createdAt;
+    private LocalDateTime updatedAt;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "member_id")
+    private MemberEntity member;
+
+    // post를 삭제하면 댓글도 같이 삭제
+    @OneToMany(mappedBy = "postEntity", cascade = CascadeType.ALL, orphanRemoval = true)
+    private List<CommentEntity> comments = new ArrayList<>();
+
+    @OneToMany(mappedBy = "post", cascade = CascadeType.ALL, orphanRemoval = true)
+    private List<LikeEntity> likes = new ArrayList<>();
+
+    @PrePersist
+    protected void onCreate() {
+        this.createdAt = LocalDateTime.now();
+        this.updatedAt = LocalDateTime.now();
+    }
+
+    @PreUpdate
+    protected void onUpdated() {
+        this.updatedAt = LocalDateTime.now();
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/entity/explanation b/src/main/java/com/example/devSns/entity/explanation
new file mode 100644
index 0000000..402a31e
--- /dev/null
+++ b/src/main/java/com/example/devSns/entity/explanation
@@ -0,0 +1,22 @@
+데이터베이스와 직접적으로 맞닿는 핵심적인 클래스
+- entity를 기준으로 테이블 생성
+- Builder 패턴을 사용해서 필요한 값만 넣음
+
+PostEntity 객체가 곧 DB의 한 행(row)
+-> 기본 키는 id이고, 나머지는 속성임을 명시하는 클래스
+
+@Entity
+데이터베이스 테이블과 매핑
+- JPA가 이 클래스를 테이블로 인식
+- 데이터베이스 테이블로 매핑할 수 있게 함
+
+@Id
+해당 필드가 기본 키임을 나타냄
+- JPA에서 이 필드는 각 행을 고유하게 식별하는 기준
+
+@GeneratedValue
+기본 키의 값을 자동 생성할 때 어떤 전략을 쓸지 지정
+GenerationType.IDENTITY는 자동 증가
+
+@Getter, @Setter (Lombok)
+보일러플레이트 제거
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/repository/CommentRepository.java b/src/main/java/com/example/devSns/repository/CommentRepository.java
new file mode 100644
index 0000000..3bc9d09
--- /dev/null
+++ b/src/main/java/com/example/devSns/repository/CommentRepository.java
@@ -0,0 +1,7 @@
+package com.example.devSns.repository;
+
+import com.example.devSns.entity.CommentEntity;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface CommentRepository extends JpaRepository<CommentEntity, Long> {
+}
diff --git a/src/main/java/com/example/devSns/repository/LikeRepository.java b/src/main/java/com/example/devSns/repository/LikeRepository.java
new file mode 100644
index 0000000..c84eb53
--- /dev/null
+++ b/src/main/java/com/example/devSns/repository/LikeRepository.java
@@ -0,0 +1,23 @@
+package com.example.devSns.repository;
+
+import com.example.devSns.entity.LikeEntity;
+import com.example.devSns.entity.MemberEntity;
+import com.example.devSns.entity.PostEntity;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.List;
+import java.util.Optional;
+
+public interface LikeRepository extends JpaRepository<LikeEntity, Long> {
+    // 특정 멤버가 특정 게시글에 좋아요 눌렀는지 확인
+    Optional<LikeEntity> findByMemberAndPost(MemberEntity member, PostEntity postEntity);
+
+    // 특정 게시글 전체 좋아요 조회
+    List<LikeEntity> findByPost(PostEntity post);
+
+    // 특정 멤버가 누른 모든 좋아요 조회
+    List<LikeEntity> findByMember(MemberEntity member);
+
+    // 좋아요 개수 조회
+    int countByPostId(Long postId);
+}
diff --git a/src/main/java/com/example/devSns/repository/MemberRepository.java b/src/main/java/com/example/devSns/repository/MemberRepository.java
new file mode 100644
index 0000000..21050d8
--- /dev/null
+++ b/src/main/java/com/example/devSns/repository/MemberRepository.java
@@ -0,0 +1,10 @@
+package com.example.devSns.repository;
+
+import com.example.devSns.entity.MemberEntity;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.List;
+
+public interface MemberRepository extends JpaRepository<MemberEntity, Long> {
+    List<MemberEntity> findByUsernameContaining(String keyword);
+}
diff --git a/src/main/java/com/example/devSns/repository/PostRepository.java b/src/main/java/com/example/devSns/repository/PostRepository.java
new file mode 100644
index 0000000..d6e24c5
--- /dev/null
+++ b/src/main/java/com/example/devSns/repository/PostRepository.java
@@ -0,0 +1,7 @@
+package com.example.devSns.repository;
+
+import com.example.devSns.entity.PostEntity;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface PostRepository extends JpaRepository<PostEntity, Long> {
+}
diff --git a/src/main/java/com/example/devSns/repository/explanation b/src/main/java/com/example/devSns/repository/explanation
new file mode 100644
index 0000000..235ff10
--- /dev/null
+++ b/src/main/java/com/example/devSns/repository/explanation
@@ -0,0 +1,5 @@
+데이터베이스 접근 (JPA 인터페이스)
+
+PostRepository<T, ID>
+상속만 하면 기본 CRUD가 다 생김
+- save, findAll, findById, deleteById
diff --git a/src/main/java/com/example/devSns/service/CommentService.java b/src/main/java/com/example/devSns/service/CommentService.java
new file mode 100644
index 0000000..0246c4e
--- /dev/null
+++ b/src/main/java/com/example/devSns/service/CommentService.java
@@ -0,0 +1,63 @@
+package com.example.devSns.service;
+
+import com.example.devSns.dto.CommentRequest;
+import com.example.devSns.dto.CommentResponse;
+import com.example.devSns.entity.CommentEntity;
+import com.example.devSns.entity.PostEntity;
+import com.example.devSns.repository.CommentRepository;
+import com.example.devSns.repository.PostRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+
+@Service
+@Transactional(readOnly = true)
+public class CommentService {
+    private final CommentRepository commentRepository;
+    private final PostRepository postRepository;
+
+    public CommentService(CommentRepository commentRepository, PostRepository postRepository) {
+        this.commentRepository = commentRepository;
+        this.postRepository = postRepository;
+    }
+
+    // 특정 게시글 댓글 조회
+    public List<CommentResponse> getCommentsByPost(Long postId) {
+        PostEntity postEntity = postRepository.findById(postId).orElseThrow();
+        return postEntity.getComments().stream()
+                .map(comment -> new CommentResponse(
+                        comment.getId(),
+                        comment.getUsername(),
+                        comment.getContent(),
+                        comment.getCreatedAt().toString()
+                ))
+                .toList();
+    }
+
+    // 댓글 생성
+    @Transactional
+    public CommentResponse createComment(Long postId, CommentRequest request) {
+        PostEntity postEntity = postRepository.findById(postId).orElseThrow();
+        CommentEntity comment = CommentEntity.create(
+                postEntity,
+                request.getUsername(),
+                request.getContent()
+        );
+
+        commentRepository.save(comment);
+
+        return new CommentResponse(
+                comment.getId(),
+                comment.getUsername(),
+                comment.getContent(),
+                comment.getCreatedAt().toString()
+        );
+    }
+
+    // 댓글 삭제
+    @Transactional
+    public void deleteComment(Long id) {
+        commentRepository.deleteById(id);
+    }
+}
diff --git a/src/main/java/com/example/devSns/service/LikeService.java b/src/main/java/com/example/devSns/service/LikeService.java
new file mode 100644
index 0000000..1dfcfbc
--- /dev/null
+++ b/src/main/java/com/example/devSns/service/LikeService.java
@@ -0,0 +1,48 @@
+package com.example.devSns.service;
+
+import com.example.devSns.entity.LikeEntity;
+import com.example.devSns.entity.MemberEntity;
+import com.example.devSns.entity.PostEntity;
+import com.example.devSns.repository.LikeRepository;
+import com.example.devSns.repository.MemberRepository;
+import com.example.devSns.repository.PostRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@Transactional
+public class LikeService {
+    private final MemberRepository memberRepository;
+    private final PostRepository postRepository;
+    private final LikeRepository likeRepository;
+
+    public LikeService(MemberRepository memberRepository, PostRepository postRepository, LikeRepository likeRepository) {
+        this.memberRepository = memberRepository;
+        this.postRepository = postRepository;
+        this.likeRepository = likeRepository;
+    }
+
+    // 좋아요 클릭
+    public void like(Long postId, Long memberId) {
+        MemberEntity member = memberRepository.findById(memberId).orElseThrow();
+        PostEntity postEntity = postRepository.findById(postId).orElseThrow();
+
+        // 중복 체크
+        likeRepository.findByMemberAndPost(member, postEntity).ifPresent(like -> {
+            throw new IllegalStateException("이미 좋아요를 눌렀습니다.");
+        });
+
+        likeRepository.save(LikeEntity.create(member, postEntity));
+    }
+
+    // 좋아요 취소
+    public void cancel(Long postId, Long memberId) {
+        MemberEntity member = memberRepository.findById(memberId).orElseThrow();
+        PostEntity postEntity = postRepository.findById(postId).orElseThrow();
+
+        LikeEntity like = likeRepository.findByMemberAndPost(member, postEntity)
+                .orElseThrow(() -> new IllegalStateException("좋아요를 누른 적이 없습니다."));
+
+        likeRepository.delete(like);
+    }
+}
diff --git a/src/main/java/com/example/devSns/service/MemberService.java b/src/main/java/com/example/devSns/service/MemberService.java
new file mode 100644
index 0000000..5597b4b
--- /dev/null
+++ b/src/main/java/com/example/devSns/service/MemberService.java
@@ -0,0 +1,58 @@
+package com.example.devSns.service;
+
+import com.example.devSns.entity.CommentEntity;
+import com.example.devSns.entity.LikeEntity;
+import com.example.devSns.entity.MemberEntity;
+import com.example.devSns.entity.PostEntity;
+import com.example.devSns.repository.MemberRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+
+@Service
+@Transactional
+public class MemberService {
+    private final MemberRepository memberRepository;
+
+    public MemberService(MemberRepository memberRepository) {
+        this.memberRepository = memberRepository;
+    }
+
+    // 멤버 생성
+    public MemberEntity createMember(String username, String email) {
+        MemberEntity member = MemberEntity.create(username, email);
+        return memberRepository.save(member);
+    }
+
+    // 단건 조회
+    public MemberEntity getMember(Long id) {
+        return memberRepository.findById(id).orElseThrow();
+    }
+
+    // 검색
+    public List<MemberEntity> search(String keyword) {
+        return memberRepository.findByUsernameContaining(keyword);
+    }
+
+    // 멤버의 게시글 조회
+    public List<PostEntity> getMemberPosts(Long id) {
+        return getMember(id).getPosts();
+    }
+
+    // 멤버의 댓글 조회
+    public List<CommentEntity> getMemberComments(Long id) {
+        return getMember(id).getComments();
+    }
+
+    // 멤버가 누른 좋아요 목록
+    public List<LikeEntity> getMemberLikes(Long id) {
+        return getMember(id).getLikes();
+    }
+
+    // 멤버 조회
+    public List<MemberEntity> getAllMembers() {
+        return memberRepository.findAll();
+    }
+
+}
diff --git a/src/main/java/com/example/devSns/service/PostService.java b/src/main/java/com/example/devSns/service/PostService.java
new file mode 100644
index 0000000..c66c5cb
--- /dev/null
+++ b/src/main/java/com/example/devSns/service/PostService.java
@@ -0,0 +1,46 @@
+package com.example.devSns.service;
+
+import com.example.devSns.entity.PostEntity;
+import com.example.devSns.repository.PostRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+
+@Service
+@Transactional(readOnly = true)
+public class PostService {
+    private final PostRepository postRepository;
+
+    // 생성자
+    public PostService(PostRepository postRepository) {
+        this.postRepository = postRepository;
+    }
+
+    public List<PostEntity> getAllPosts() {
+        return postRepository.findAll();
+    }
+
+    public PostEntity getPost(Long id) {
+        return postRepository.findById(id).orElseThrow();
+    }
+
+    @Transactional
+    public PostEntity createPost(PostEntity postEntity) {
+        return postRepository.save(postEntity);
+    }
+
+    @Transactional
+    public PostEntity updatePost(Long id, PostEntity updated) {
+        PostEntity postEntity = postRepository.findById(id).orElseThrow();
+        postEntity.setTitle(updated.getTitle());
+        postEntity.setContent(updated.getContent());
+        return postRepository.save(postEntity);
+    }
+
+    @Transactional
+    public void deletePost(Long id) {
+        postRepository.deleteById(id);
+    }
+
+}
\ No newline at end of file
diff --git a/src/main/java/com/example/devSns/service/explanation b/src/main/java/com/example/devSns/service/explanation
new file mode 100644
index 0000000..09b39f6
--- /dev/null
+++ b/src/main/java/com/example/devSns/service/explanation
@@ -0,0 +1,33 @@
+비지니스 로직 담당
+
+PostService
+
+@Service
+비지니스 로직이 모이는 곳
+- 트랜잭션을 붙여야 할 때도 주로 서비스에서
+- 의존성 주입 (생성자 주입)
+
+@Transactional(readOnly = true)
+읽기 성능 최적화
+- 원자성 보장
+- 안전빵
+
+private final PostRepository postRepository;
+- 의존성으로 받는 레포지토리
+- 생성자 주입
+- JpaRepository<PostEntity, Long> 상속
+
+findAll()
+- 모든 게시글 조회
+
+findById()
+- getPost 함수에서 PK(id)로 단건 조회
+- updatePost 함수에서 수정 대상 로드, 필드 갱신, 저장
+
+save
+- 새 엔터티 저장
+- id가 없으면 persist, 있으면 merge
+
+deleteById
+- PK(id)로 삭제
+
diff --git a/src/main/resources/application.properties b/src/main/resources/application.properties
index f3f10af..e782abf 100644
--- a/src/main/resources/application.properties
+++ b/src/main/resources/application.properties
@@ -1 +1,19 @@
 spring.application.name=devSns
+
+# ?? ??
+server.port=8080
+
+# MySQL
+spring.datasource.url=jdbc:mysql://localhost:3306/devSns?serverTimezone=Asia/Seoul&characterEncoding=UTF-8
+spring.datasource.username=root
+spring.datasource.password=as112525@
+spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
+
+# JPA
+spring.jpa.hibernate.ddl-auto=update
+spring.jpa.show-sql=true
+spring.jpa.properties.hibernate.format_sql=true
+
+# Thymeleaf
+spring.thymeleaf.cache=false
+
diff --git a/src/main/resources/templates/detail.html b/src/main/resources/templates/detail.html
new file mode 100644
index 0000000..b99d7ba
--- /dev/null
+++ b/src/main/resources/templates/detail.html
@@ -0,0 +1,116 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+    <!-- 제목 / 내용 -->
+    <h2 th:text="${post.title}">제목</h2>
+    <h2 th:text="${post.content}">내용</h2>
+    <p>
+        <b>작성자:</b>
+        <span th:text="${post.author}"></span>
+    </p>
+
+    <!-- 수정 / 삭제 버튼 -->
+    <a th:href="@{|/posts/${post.id}/edit|}">
+        <button type="button">수정</button>
+    </a>
+    <form th:action="@{|/posts/${post.id}/delete|}" method="post">
+        <button type="submit">삭제</button>
+    </form>
+    <a th:href="@{|/posts|}">
+        <button type="button">게시글 보기</button>
+    </a>
+
+    <!-- 좋아요 -->
+    <hr/>
+
+    <div>
+        <button id="like-btn"
+                th:data-post-id="${post.id}"
+                th:data-member-id="${memberId}"
+                th:classappend="${liked} ? ' liked' : ''"
+                style="border:none; background:none; cursor:pointer; font-size:18px;">
+            <span id="like-icon" th:text="${liked} ? '❤️' : '🤍'"></span>
+            <span id="like-count" th:text="${likeCount}"></span>
+        </button>
+    </div>
+
+    <hr/>
+
+    <!-- 댓글 -->
+    <hr />
+    <h3>댓글</h3>
+
+    <div th:if="${#lists.isEmpty(post.comments)}">
+        <p>댓글이 없습니다.</p>
+    </div>
+
+    <ul th:if="${!#lists.isEmpty(post.comments)}">
+        <li th:each="comment : ${post.comments}">
+            <p><b th:text="${comment.username}"></b></p>
+            <p th:text="${comment.content}"></p>
+            <p>작성일:
+                <small th:text="${#temporals.format(comment.createdAt, 'yyyy-MM-dd HH:mm')}"></small>
+            </p>
+
+            <form th:action="@{'/comments/' + ${comment.id} + '/delete'}" method="post">
+                <input type="hidden" name="postId" th:value="${post.id}">
+                <button type="submit">댓글 삭제</button>
+            </form>
+
+            <hr/>
+        </li>
+    </ul>
+
+    <hr />
+
+    <!-- 댓글 작성 -->
+    <h3>댓글 작성하기</h3>
+
+    <form th:action="@{'/comments/' + ${post.id}}" method="post">
+        <p>
+            작성자:
+            <input type="text" name="username" required />
+        </p>
+        <p>
+            내용:<br/>
+            <textarea name="content" rows="4" cols="50" required></textarea>
+        </p>
+
+        <button type="submit">댓글 등록</button>
+    </form>
+
+    <!-- 좋아요 Ajax 스크럽트 -->
+    <script>
+        document.addEventListener("DOMContentLoaded", function () {
+            const btn = document.getElementById("like-btn");
+
+            btn.addEventListener("click", async function () {
+                const postId = btn.dataset.postId;
+                const memberId = btn.dataset.memberId;
+
+                const likedNow = btn.classList.contains("liked");
+                const method = likedNow ? "DELETE" : "POST";
+
+                const res = await fetch(`/posts/${postId}/like?memberId=${memberId}`, {
+                    method: method
+                });
+
+                const data = await res.json();
+
+                // UI 업데이트(좋아요 수)
+                document.getElementById("like-count").textContent = data.likeCount;
+
+                // UI 업데이트(하트 아이콘)
+                if (data.liked) {
+                    btn.classList.add("liked");
+                    document.getElementById("like-icon").textContent = "❤️";
+                } else {
+                    btn.classList.remove("liked");
+                    document.getElementById("like-icon").textContent = "🤍";
+                }
+            });
+        });
+    </script>
+
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/edit.html b/src/main/resources/templates/edit.html
new file mode 100644
index 0000000..777a6e3
--- /dev/null
+++ b/src/main/resources/templates/edit.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+    <h2>게시글 수정</h2>
+
+    <form th:action="@{|/posts/${post.id}/update|}" method="post" th:object="${post}">
+        <label>제목:</label><br/>
+        <input type="text" th:field="*{title}" /><br/><br/>
+
+        <label>내용:</label><br/>
+        <textarea th:field="*{content}" rows="6" cols="40"></textarea><br/><br/>
+
+        <button type="submit">수정 완료</button>
+    </form>
+
+    <br/>
+    <a th:href="@{|/posts/${post.id}|}">취소</a>
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/form.html b/src/main/resources/templates/form.html
new file mode 100644
index 0000000..52849d8
--- /dev/null
+++ b/src/main/resources/templates/form.html
@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+    <h2>새 글 작성</h2>
+    <form action="/posts" method="post" th:object="${post}">
+        <input type="text" th:field="*{title}" placeholder="제목" />
+        <textarea th:field="*{content}" placeholder="내용"></textarea>
+        <input type="text" th:field="*{author}" placeholder="작성자" />
+        <button type="submit">저장</button>
+    </form>
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/list.html b/src/main/resources/templates/list.html
new file mode 100644
index 0000000..62c5d7e
--- /dev/null
+++ b/src/main/resources/templates/list.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+    <h2>게시판</h2>
+    <a href="/posts/new">새 글 쓰기</a>
+    <ul>
+        <li th:each="post : ${posts}">
+            <a th:href="@{|/posts/${post.id}|}" th:text="${post.title}"></a>
+            </br>
+            <small>
+                작성일:
+                <span th:text="${#temporals.format(post.createdAt, 'yyyy-MM-dd HH:mm')}"></span>
+                /
+                수정일:
+                <span th:text="${#temporals.format(post.updatedAt, 'yyyy-MM-dd HH:mm')}"></span>
+            </small>
+        </li>
+    </ul>
+    <a href="/members">
+        <button type="button">멤버 목록 보기</button>
+    </a>
+</body>
diff --git a/src/main/resources/templates/member-detail.html b/src/main/resources/templates/member-detail.html
new file mode 100644
index 0000000..77de7d8
--- /dev/null
+++ b/src/main/resources/templates/member-detail.html
@@ -0,0 +1,45 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+
+<h2 th:text="${member.username} + '님의 프로필'"></h2>
+<p>
+    이메일: <b th:text="${member.email}"></b><br/>
+    가입일: <span th:text="${#temporals.format(member.createdAt, 'yyyy-MM-dd HH:mm')}"></span>
+</p>
+
+<hr/>
+
+<h3>작성한 게시글</h3>
+<div th:if="${#lists.isEmpty(posts)}">
+    <p>작성한 게시글이 없습니다.</p>
+</div>
+
+<ul th:if="${!#lists.isEmpty(posts)}">
+    <li th:each="p : ${posts}">
+        <a th:href="@{|/posts/${p.id}|}" th:text="${p.title}"></a>
+        (작성일: <span th:text="${#temporals.format(p.createdAt, 'yyyy-MM-dd HH:mm')}"></span>)
+    </li>
+</ul>
+
+<hr/>
+
+<h3>작성한 댓글</h3>
+<div th:if="${#lists.isEmpty(comments)}">
+    <p>작성한 댓글이 없습니다.</p>
+</div>
+
+<ul th:if="${!#lists.isEmpty(comments)}">
+    <li th:each="c : ${comments}">
+        <b th:text="${c.username}"></b> :
+        <span th:text="${c.content}"></span>
+        <small>(<span th:text="${#temporals.format(c.createdAt, 'yyyy-MM-dd HH:mm')}"></span>)</small>
+    </li>
+</ul>
+
+<hr/>
+
+<a href="/members">전체 멤버 목록</a>
+
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/member-form.html b/src/main/resources/templates/member-form.html
new file mode 100644
index 0000000..d777c99
--- /dev/null
+++ b/src/main/resources/templates/member-form.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+
+<h2>새 멤버 생성</h2>
+
+<form action="/members" method="post">
+    <p>
+        이름: <input type="text" name="username" required>
+    </p>
+
+    <p>
+        이메일: <input type="email" name="email" required>
+    </p>
+
+    <button type="submit">등록</button>
+</form>
+
+<hr/>
+<a href="/members">전체 멤버 목록 보기</a>
+
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/member-list.html b/src/main/resources/templates/member-list.html
new file mode 100644
index 0000000..03c7934
--- /dev/null
+++ b/src/main/resources/templates/member-list.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+<h2>전체 멤버 목록</h2>
+
+<a href="/members/new">새 멤버 만들기</a>
+
+<form action="/members/search" method="get">
+    <input type="text" name="keyword" placeholder="검색(이름)">
+    <button type="submit">검색</button>
+</form>
+
+<hr/>
+
+<ul>
+    <li th:each="m : ${members}">
+        <a th:href="@{|/members/${m.id}|}"
+           th:text="${m.username}"></a>
+        ( <span th:text="${m.email}"></span> )
+    </li>
+</ul>
+
+<a href="/posts">게시글 목록</a>
+
+</body>
+</html>
\ No newline at end of file
diff --git a/src/main/resources/templates/member-search.html b/src/main/resources/templates/member-search.html
new file mode 100644
index 0000000..2c70fce
--- /dev/null
+++ b/src/main/resources/templates/member-search.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<body>
+
+<h2 th:text="'검색 결과: ' + ${keyword}"></h2>
+
+<form action="/members/search" method="get">
+    <input type="text" name="keyword" placeholder="검색(이름)" th:value="${keyword}">
+    <button type="submit">검색</button>
+</form>
+
+<hr/>
+
+<div th:if="${#lists.isEmpty(members)}">
+    <p>검색 결과가 없습니다.</p>
+</div>
+
+<ul th:if="${!#lists.isEmpty(members)}">
+    <li th:each="m : ${members}">
+        <a th:href="@{|/members/${m.id}|}"
+           th:text="${m.username}"></a>
+        ( <span th:text="${m.email}"></span> )
+    </li>
+</ul>
+
+<a href="/members">멤버 목록으로</a>
+
+</body>
+</html>
\ No newline at end of file