diff --git a/src/main/kotlin/io/devchw/coderabbit/BoardController.kt b/src/main/kotlin/io/devchw/coderabbit/BoardController.kt
new file mode 100644
index 0000000..0f89dac
--- /dev/null
+++ b/src/main/kotlin/io/devchw/coderabbit/BoardController.kt
@@ -0,0 +1,111 @@
+package io.devchw.coderabbit
+
+import org.springframework.http.HttpStatus
+import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.DeleteMapping
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.PathVariable
+import org.springframework.web.bind.annotation.PostMapping
+import org.springframework.web.bind.annotation.PutMapping
+import org.springframework.web.bind.annotation.RequestBody
+import org.springframework.web.bind.annotation.RequestMapping
+import org.springframework.web.bind.annotation.RestController
+import java.util.concurrent.atomic.AtomicLong
+import org.springframework.beans.factory.annotation.Autowired
+
+/**
+ * @author DevCHW
+ * @since 2025-06-05
+ */
+@RestController
+@RequestMapping("/api/board")
+class BoardController(
+    @Autowired private val commentController: CommentController
+) {
+
+    private val posts = mutableMapOf<Long, Post>()
+    private val idGenerator = AtomicLong(1)
+
+    /**
+     * Creates a new post, assigns it a unique ID, and stores it in memory.
+     *
+     * @param post The post data to create.
+     * @return The created post with its assigned ID and HTTP status 201 (Created).
+     */
+    @PostMapping
+    fun createPost(@RequestBody post: Post): ResponseEntity<Post> {
+        val id = idGenerator.getAndIncrement()
+        post.id = id
+        posts[id] = post
+        return ResponseEntity.status(HttpStatus.CREATED).body(post)
+    }
+
+    /**
+     * Retrieves a list of all posts.
+     *
+     * @return HTTP 200 response containing all stored posts.
+     */
+    @GetMapping
+    fun getPosts(): ResponseEntity<List<Post>> {
+        return ResponseEntity.ok(posts.values.toList())
+    }
+
+    /**
+     * Retrieves a post by its unique ID.
+     *
+     * Returns the post with HTTP 200 if found, or HTTP 404 if no post exists with the given ID.
+     *
+     * @param id The unique identifier of the post to retrieve.
+     * @return A ResponseEntity containing the post if found, or a 404 status if not.
+     */
+    @GetMapping("/{id}")
+    fun getPost(@PathVariable id: Long): ResponseEntity<Post> {
+        val post = posts[id]
+        return if (post != null) {
+            ResponseEntity.ok(post)
+        } else {
+            ResponseEntity.status(HttpStatus.NOT_FOUND).build()
+        }
+    }
+
+    /**
+     * Updates an existing post with new data by its ID.
+     *
+     * If the post with the specified ID does not exist, returns HTTP 404 (Not Found).
+     * Otherwise, replaces the post's content and returns the updated post with HTTP 200 (OK).
+     *
+     * @param id The ID of the post to update.
+     * @param updatedPost The new post data to replace the existing post.
+     * @return The updated post with HTTP 200, or HTTP 404 if the post does not exist.
+     */
+    @PutMapping("/{id}")
+    fun updatePost(@PathVariable id: Long, @RequestBody updatedPost: Post): ResponseEntity<Post> {
+        if (!posts.containsKey(id)) {
+            return ResponseEntity.status(HttpStatus.NOT_FOUND).build()
+        }
+        updatedPost.id = id
+        posts[id] = updatedPost
+        return ResponseEntity.ok(updatedPost)
+    }
+
+    /**
+     * Deletes a post by its ID.
+     *
+     * Removes the post with the specified ID from the in-memory store. Returns HTTP 204 (No Content) if the post was deleted, or HTTP 404 (Not Found) if the post does not exist.
+     *
+     * @param id The unique identifier of the post to delete.
+     * @return A ResponseEntity with HTTP status 204 if successful, or 404 if the post is not found.
+     */
+    @DeleteMapping("/{id}")
+    fun deletePost(@PathVariable id: Long): ResponseEntity<Void> {
+        if (!posts.containsKey(id)) {
+            return ResponseEntity.status(HttpStatus.NOT_FOUND).build()
+        }
+
+        // 게시물과 관련된 모든 댓글 삭제
+        commentController.deleteAllCommentsForPost(id)
+
+        posts.remove(id)
+        return ResponseEntity.status(HttpStatus.NO_CONTENT).build()
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/io/devchw/coderabbit/Comment.kt b/src/main/kotlin/io/devchw/coderabbit/Comment.kt
new file mode 100644
index 0000000..b05db28
--- /dev/null
+++ b/src/main/kotlin/io/devchw/coderabbit/Comment.kt
@@ -0,0 +1,11 @@
+package io.devchw.coderabbit
+
+/**
+ * @author DevCHW
+ * @since 2025-06-05
+ */
+data class Comment(
+    var id: Long? = null,
+    var postId: Long,
+    var content: String
+)
diff --git a/src/main/kotlin/io/devchw/coderabbit/CommentController.kt b/src/main/kotlin/io/devchw/coderabbit/CommentController.kt
new file mode 100644
index 0000000..5801046
--- /dev/null
+++ b/src/main/kotlin/io/devchw/coderabbit/CommentController.kt
@@ -0,0 +1,86 @@
+package io.devchw.coderabbit
+
+import org.springframework.http.HttpStatus
+import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.*
+import java.util.concurrent.atomic.AtomicLong
+
+/**
+ * @author DevCHW
+ * @since 2025-06-05
+ */
+@RestController
+@RequestMapping("/api/board")
+class CommentController {
+
+    private val comments = mutableMapOf<Long, Comment>()
+    private val idGenerator = AtomicLong(1)
+
+    // 댓글 생성
+    @PostMapping("/{postId}/comments")
+    fun createComment(
+        @PathVariable postId: Long, 
+        @RequestBody comment: Comment
+    ): ResponseEntity<Comment> {
+        val id = idGenerator.getAndIncrement()
+        comment.id = id
+        comment.postId = postId
+        comments[id] = comment
+        return ResponseEntity.status(HttpStatus.CREATED).body(comment)
+    }
+
+    // 게시물의 모든 댓글 조회
+    @GetMapping("/{postId}/comments")
+    fun getCommentsByPost(@PathVariable postId: Long): ResponseEntity<List<Comment>> {
+        val postComments = comments.values.filter { it.postId == postId }
+        return ResponseEntity.ok(postComments)
+    }
+
+    // 댓글 상세 조회
+    @GetMapping("/comments/{commentId}")
+    fun getComment(@PathVariable commentId: Long): ResponseEntity<Comment> {
+        val comment = comments[commentId]
+        return if (comment != null) {
+            ResponseEntity.ok(comment)
+        } else {
+            ResponseEntity.status(HttpStatus.NOT_FOUND).build()
+        }
+    }
+
+    // 댓글 수정
+    @PutMapping("/comments/{commentId}")
+    fun updateComment(
+        @PathVariable commentId: Long, 
+        @RequestBody updatedComment: Comment
+    ): ResponseEntity<Comment> {
+        val existingComment = comments[commentId]
+        if (existingComment == null) {
+            return ResponseEntity.status(HttpStatus.NOT_FOUND).build()
+        }
+
+        // 기존 postId 유지
+        updatedComment.id = commentId
+        updatedComment.postId = existingComment.postId
+        comments[commentId] = updatedComment
+        return ResponseEntity.ok(updatedComment)
+    }
+
+    // 댓글 삭제
+    @DeleteMapping("/comments/{commentId}")
+    fun deleteComment(@PathVariable commentId: Long): ResponseEntity<Void> {
+        if (!comments.containsKey(commentId)) {
+            return ResponseEntity.status(HttpStatus.NOT_FOUND).build()
+        }
+        comments.remove(commentId)
+        return ResponseEntity.status(HttpStatus.NO_CONTENT).build()
+    }
+
+    // 게시물의 모든 댓글 삭제 (게시물이 삭제될 때 호출)
+    fun deleteAllCommentsForPost(postId: Long) {
+        val commentIdsToRemove = comments.values
+            .filter { it.postId == postId }
+            .mapNotNull { it.id }
+
+        commentIdsToRemove.forEach { comments.remove(it) }
+    }
+}
diff --git a/src/main/kotlin/io/devchw/coderabbit/Post.kt b/src/main/kotlin/io/devchw/coderabbit/Post.kt
new file mode 100644
index 0000000..01a9d14
--- /dev/null
+++ b/src/main/kotlin/io/devchw/coderabbit/Post.kt
@@ -0,0 +1,12 @@
+package io.devchw.coderabbit
+
+/**
+ * @author DevCHW
+ * @since 2025-06-05
+ */
+data class Post(
+    var id: Long? = null,
+    var title: String,
+    var content: String,
+    var comments: MutableList<Comment> = mutableListOf()
+)