diff --git a/README.md b/README.md
index b8e45af..76f9e11 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,2 @@
-# backend
-도서 성취도 기록 서비스 backend 저장소입니다.
+# backend
+도서 성취도 기록 서비스 backend 저장소입니다.
diff --git a/src/main/java/com/bookmile/backend/domain/group/controller/GroupController.java b/src/main/java/com/bookmile/backend/domain/group/controller/GroupController.java
index 9a98fb0..bd30e54 100644
--- a/src/main/java/com/bookmile/backend/domain/group/controller/GroupController.java
+++ b/src/main/java/com/bookmile/backend/domain/group/controller/GroupController.java
@@ -6,11 +6,12 @@
 import com.bookmile.backend.domain.group.service.GroupService;
 import com.bookmile.backend.domain.group.service.Impl.GroupMemberServiceImpl;
 import com.bookmile.backend.global.common.CommonResponse;
-import com.bookmile.backend.domain.user.entity.User;
 import io.swagger.v3.oas.annotations.Operation;
 import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.security.core.userdetails.UserDetails;
 import org.springframework.web.bind.annotation.*;
 
 import java.util.List;
@@ -33,13 +34,12 @@ public class GroupController {
     @PostMapping
     public ResponseEntity<CommonResponse<GroupCreateResponseDto>> createGroup(
             @RequestBody @Valid GroupCreateRequestDto requestDto,
-            @RequestParam Long userId // userId를 직접 받음
+            @AuthenticationPrincipal UserDetails userDetails
     ) {
-        // User 정보를 UserRepository에서 조회
-        User user = groupService.getUserById(userId);
+        String userEmail = userDetails.getUsername();
 
         // 그룹 생성 요청 처리
-        GroupCreateResponseDto responseDto = groupService.createGroup(requestDto, user);
+        GroupCreateResponseDto responseDto = groupService.createGroup(requestDto, userEmail);
         return ResponseEntity.status(GROUP_CREATE.getStatus())
                 .body(CommonResponse.from(GROUP_CREATE.getMessage(), responseDto));
     }
@@ -47,12 +47,13 @@ public ResponseEntity<CommonResponse<GroupCreateResponseDto>> createGroup(
     @Operation(summary = "그룹 참여하기", description = "이미 존재하는 그룹에 참여합니다. 참여한 유저는 자동으로 MEMBER 역할을 부여받으며 비공개 그룹의 경우 비밀번호가 필요합니다. <br>"
     + "공개 그룹의 경우 비밀번호를 null 값이 아닌 공백(그냥 띄어쓰기 한 칸)으로 입력해주세요")
     @PostMapping("/{groupId}")
-    public ResponseEntity<CommonResponse<Void>> joinGroup(
+    public ResponseEntity<CommonResponse<GroupJoinResponseDto>> joinGroup(
             @RequestBody @Valid GroupJoinRequestDto requestDto,
-            @RequestHeader("user_id") Long userId
+            @AuthenticationPrincipal UserDetails userDetails
     ) {
-        groupJoinService.joinGroup(userId, requestDto);
-        return ResponseEntity.ok(CommonResponse.from(GROUP_JOIN.getMessage(), null));
+        String userEmail = userDetails.getUsername();
+        GroupJoinResponseDto responseDto = groupJoinService.joinGroup(userEmail, requestDto);
+        return ResponseEntity.ok(CommonResponse.from(GROUP_JOIN.getMessage(), responseDto));
     }
 
     @Operation(summary = "그룹 멤버 조회"
@@ -67,9 +68,12 @@ public ResponseEntity<List<GroupMemberResponseDto>> getMembers(@PathVariable Lon
             , description = "그룹 상태를 변경합니다. 그룹장만이 변경할 수 있습니다.")
     @PatchMapping("/{groupId}")
     public ResponseEntity<GroupStatusUpdateResponseDto> updateGroupStatus(
-            @PathVariable Long groupId,@RequestBody @Valid GroupStatusUpdateRequestDto requestDto
+            @PathVariable Long groupId,
+            @RequestBody @Valid GroupStatusUpdateRequestDto requestDto,
+            @AuthenticationPrincipal UserDetails userDetails
     ) {
-        GroupStatusUpdateResponseDto responseDto = groupService.updateGroupStatus(groupId, requestDto, requestDto.getUserId());
+        String userEmail = userDetails.getUsername();
+        GroupStatusUpdateResponseDto responseDto = groupService.updateGroupStatus(groupId, requestDto, userEmail);
         return ResponseEntity.ok(responseDto);
     }
 
@@ -115,9 +119,11 @@ public ResponseEntity<GroupDetailResponseDto> getGroupDetail(@PathVariable Long
     @Operation(summary = "그룹 공개/비공개 전환", description = "그룹장은 그룹 공개여부를 변경할 수 있습니다.")
     public ResponseEntity<CommonResponse<Object>> updateGroupVisibility(
             @PathVariable Long groupId,
-            @RequestBody @Valid GroupPrivateRequestDto requestDto
+            @RequestBody @Valid GroupPrivateRequestDto requestDto,
+            @AuthenticationPrincipal UserDetails userDetails
     ) {
-        groupService.updateGroupPrivate(groupId, requestDto.getIsOpen(), requestDto.getUserId());
+        String userEmail = userDetails.getUsername();
+        groupService.updateGroupPrivate(groupId, requestDto.getIsOpen(), userEmail);
         return ResponseEntity.ok(CommonResponse.from(GROUP_PRIVATE_UPDATE.getMessage()));
     }
 }
diff --git a/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupPrivateRequestDto.java b/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupPrivateRequestDto.java
index 10d978f..a5f5d5d 100644
--- a/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupPrivateRequestDto.java
+++ b/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupPrivateRequestDto.java
@@ -6,6 +6,5 @@
 @Getter
 @NoArgsConstructor
 public class GroupPrivateRequestDto {
-    private Long userId;
     private Boolean isOpen;
 }
\ No newline at end of file
diff --git a/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupStatusUpdateRequestDto.java b/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupStatusUpdateRequestDto.java
index 27aef2b..2e8617c 100644
--- a/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupStatusUpdateRequestDto.java
+++ b/src/main/java/com/bookmile/backend/domain/group/dto/req/GroupStatusUpdateRequestDto.java
@@ -13,6 +13,4 @@ public class GroupStatusUpdateRequestDto {
     @Schema(description = "그룹 상태 (RECRUITING, IN_PROGRESS, COMPLETED)", example = "IN_PROGRESS")
     @NotNull(message = "변경할 상태는 필수입니다.")
     private GroupStatus status;
-
-    private Long userId;
 }
diff --git a/src/main/java/com/bookmile/backend/domain/group/service/GroupJoinService.java b/src/main/java/com/bookmile/backend/domain/group/service/GroupJoinService.java
index 10169e4..109ee09 100644
--- a/src/main/java/com/bookmile/backend/domain/group/service/GroupJoinService.java
+++ b/src/main/java/com/bookmile/backend/domain/group/service/GroupJoinService.java
@@ -4,5 +4,5 @@
 import com.bookmile.backend.domain.group.dto.res.GroupJoinResponseDto;
 
 public interface GroupJoinService {
-    GroupJoinResponseDto joinGroup(Long userId, GroupJoinRequestDto groupJoinRequestDto);
+    GroupJoinResponseDto joinGroup(String userEmail, GroupJoinRequestDto requestDto);
 }
diff --git a/src/main/java/com/bookmile/backend/domain/group/service/GroupService.java b/src/main/java/com/bookmile/backend/domain/group/service/GroupService.java
index e7b6938..4b5a5fa 100644
--- a/src/main/java/com/bookmile/backend/domain/group/service/GroupService.java
+++ b/src/main/java/com/bookmile/backend/domain/group/service/GroupService.java
@@ -1,7 +1,6 @@
 package com.bookmile.backend.domain.group.service;
 
 import com.bookmile.backend.domain.group.dto.req.GroupCreateRequestDto;
-import com.bookmile.backend.domain.group.dto.req.GroupSearchRequestDto;
 import com.bookmile.backend.domain.group.dto.req.GroupStatusUpdateRequestDto;
 import com.bookmile.backend.domain.group.dto.res.GroupCreateResponseDto;
 import com.bookmile.backend.domain.group.dto.res.GroupDetailResponseDto;
@@ -13,8 +12,8 @@
 
 public interface GroupService {
     User getUserById(Long userId); // User 정보 조회
-    GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, User user);
-    GroupStatusUpdateResponseDto updateGroupStatus(Long groupId, GroupStatusUpdateRequestDto requestDto, Long userId);
+    GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, String userEmail);
+    GroupStatusUpdateResponseDto updateGroupStatus(Long groupId, GroupStatusUpdateRequestDto requestDto, String userEmail);
 
     List<GroupListResponseDto> getRecruitingGroups(String isbn13);
     List<GroupListResponseDto> getInProgressGroups(String isbn13);
@@ -22,5 +21,5 @@ public interface GroupService {
 
     GroupDetailResponseDto getGroupDetail(Long groupId);
 
-    void updateGroupPrivate(Long groupId, Boolean isOpen, Long userId);
+    void updateGroupPrivate(Long groupId, Boolean isOpen, String userEmail);
 }
diff --git a/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupJoinServiceImpl.java b/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupJoinServiceImpl.java
index 6fe0200..44b6c12 100644
--- a/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupJoinServiceImpl.java
+++ b/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupJoinServiceImpl.java
@@ -6,6 +6,7 @@
 import com.bookmile.backend.domain.group.repository.GroupRepository;
 import com.bookmile.backend.domain.group.service.GroupJoinService;
 import com.bookmile.backend.domain.user.entity.User;
+import com.bookmile.backend.domain.user.repository.UserRepository;
 import com.bookmile.backend.domain.userGroup.entity.Role;
 import com.bookmile.backend.domain.userGroup.entity.UserGroup;
 import com.bookmile.backend.domain.userGroup.repository.UserGroupRepository;
@@ -20,18 +21,20 @@ public class GroupJoinServiceImpl implements GroupJoinService {
 
     private final GroupRepository groupRepository;
     private final UserGroupRepository userGroupRepository;
+    private final UserRepository userRepository;
 
     @Override
-    public GroupJoinResponseDto joinGroup(Long userId, GroupJoinRequestDto groupJoinRequestDto) {
+    public GroupJoinResponseDto joinGroup(String userEmail, GroupJoinRequestDto requestDto) {
+        User user = validateUserByEmail(userEmail);
 
-        Group group = findGroup(groupJoinRequestDto.getGroupId());
+        Group group = findGroup(requestDto.getGroupId());
 
-        checkUserAlreadyJoined(userId, group.getId());
+        checkUserAlreadyJoined(user.getId(), group.getId());
         checkGroupCapacity(group);
-        checkGroupPassword(group, groupJoinRequestDto.getPassword());
+        checkGroupPassword(group, requestDto.getPassword());
 
         UserGroup userGroup = UserGroup.builder()
-                .user(new User(userId))
+                .user(user)
                 .group(group)
                 .role(Role.MEMBER)
                 .build();
@@ -64,4 +67,9 @@ private void checkGroupPassword(Group group, String password) {
             throw new CustomException(StatusCode.INVALID_GROUP_PASSWORD);
         }
     }
+
+    private User validateUserByEmail(String email) {
+        return userRepository.findByEmail(email)
+                .orElseThrow(() -> new CustomException(StatusCode.USER_NOT_FOUND));
+    }
 }
diff --git a/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupServiceImpl.java b/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupServiceImpl.java
index 9a29755..8fb28ea 100644
--- a/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupServiceImpl.java
+++ b/src/main/java/com/bookmile/backend/domain/group/service/Impl/GroupServiceImpl.java
@@ -20,6 +20,7 @@
 import com.bookmile.backend.domain.userGroup.entity.UserGroup;
 import com.bookmile.backend.domain.userGroup.entity.Role;
 import com.bookmile.backend.domain.userGroup.repository.UserGroupRepository;
+import com.bookmile.backend.global.common.StatusCode;
 import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
 import com.bookmile.backend.global.exception.CustomException;
@@ -48,7 +49,9 @@ public User getUserById(Long userId) {
 
     @Override
     @Transactional
-    public GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, User user) {
+    public GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, String userEmail) {
+        User user = validateUserByEmail(userEmail);
+
         Book book = bookService.saveBook(requestDto.getIsbn13());
 
         Template template = checkTemplate(requestDto);
@@ -57,7 +60,7 @@ public GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, User
 
         Group group = groupRepository.save(requestDto.toEntity(book, goalType, goalContent));
 
-        Long templateId;
+        Long templateId = null;
         if (requestDto.getTemplateId() == null) {
             template = Template.builder()
                     .group(group)
@@ -65,7 +68,7 @@ public GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, User
                     .goalContent(goalContent)
                     .isTemplate(true)
                     .build();
-            templateId = template.getId();
+            templateRepository.save(template);
         } else {
             templateId = requestDto.getTemplateId();
         }
@@ -76,16 +79,17 @@ public GroupCreateResponseDto createGroup(GroupCreateRequestDto requestDto, User
 
     @Override
     @Transactional
-    public GroupStatusUpdateResponseDto updateGroupStatus(Long groupId, GroupStatusUpdateRequestDto requestDto, Long userId) {
+    public GroupStatusUpdateResponseDto updateGroupStatus(Long groupId, GroupStatusUpdateRequestDto requestDto, String userEmail) {
+        User user = validateUserByEmail(userEmail);
+
         Group group = findGroupById(groupId);
-        UserGroup userGroup = findUserGroupById(userId, groupId);
+        UserGroup userGroup = findUserGroupById(user.getId(), groupId);
 
         validateGroupMaster(userGroup);
         updateGroupStatus(group, requestDto.getStatus());
 
         return GroupStatusUpdateResponseDto.toDto(group);
     }
-
     private List<GroupListResponseDto> findGroupsByStatus(String isbn13, GroupStatus status, boolean isRecent) {
         List<Group> groups;
         if (isRecent) {
@@ -131,10 +135,11 @@ public GroupDetailResponseDto getGroupDetail(Long groupId) {
 
     @Override
     @Transactional
-    public void updateGroupPrivate(Long groupId, Boolean isOpen, Long userId) {
+    public void updateGroupPrivate(Long groupId, Boolean isOpen, String userEmail) {
+        User user = validateUserByEmail(userEmail);
         Group group = findGroupById(groupId);
 
-        UserGroup userGroup = findUserGroupById(userId, groupId);
+        UserGroup userGroup = findUserGroupById(user.getId(), groupId);
         validateGroupMaster(userGroup);
 
         group.setIsOpen(isOpen);
@@ -145,6 +150,11 @@ private Group findGroupById(Long groupId) {
                 .orElseThrow(() -> new CustomException(GROUP_NOT_FOUND));
     }
 
+    private User validateUserByEmail(String email) {
+        return userRepository.findByEmail(email)
+                .orElseThrow(() -> new CustomException(StatusCode.USER_NOT_FOUND));
+    }
+
     private UserGroup findUserGroupById(Long userId, Long groupId) {
         return userGroupRepository.findByUserIdAndGroupId(userId, groupId)
                 .orElseThrow(() -> new CustomException(NOT_MEMBER));
diff --git a/src/main/java/com/bookmile/backend/domain/userGroup/repository/UserGroupRepository.java b/src/main/java/com/bookmile/backend/domain/userGroup/repository/UserGroupRepository.java
index 1231322..7488d24 100644
--- a/src/main/java/com/bookmile/backend/domain/userGroup/repository/UserGroupRepository.java
+++ b/src/main/java/com/bookmile/backend/domain/userGroup/repository/UserGroupRepository.java
@@ -16,7 +16,7 @@ public interface UserGroupRepository extends JpaRepository<UserGroup, Long> {
 
     List<UserGroup> findByGroupId(Long groupId);
 
-    Optional<UserGroup> findByUserIdAndGroupId(Long userId, Long groupId);
+    Optional<UserGroup> findByUserIdAndGroupId(Long groupId, Long userId);
 
     @Query("SELECT ug FROM UserGroup ug WHERE ug.group.id = :groupId AND ug.role = 'MASTER'")
     Optional<UserGroup> findMasterByGroupId(@Param("groupId") Long groupId);