diff --git a/src/controllers/GroupsController.ts b/src/controllers/GroupsController.ts
index 2dcae4f..6fac2a1 100644
--- a/src/controllers/GroupsController.ts
+++ b/src/controllers/GroupsController.ts
@@ -308,6 +308,27 @@ export class GroupsController {
 		h.success("The user has been successfully invited to join the group!");
 	}
 
+	/**
+	 * Respond to a user invitation
+	 * 
+	 * @param h Request handler
+	 */
+	public static async RespondInvitation(h: RequestHandler) {
+		const groupID = await h.postGroupIDWithAccess("id", GroupsAccessLevel.LIMITED_ACCESS);
+		const accept = h.postBool("accept");
+
+		// Check if the user really received an invitation to join the group
+		if(!await GroupsHelper.ReceivedInvitation(groupID, h.getUserId()))
+			h.error(404, "Invitation not found!");
+		
+		// Respond to the invitation
+		await GroupsHelper.RespondInvitation(groupID, h.getUserId(), accept);
+
+		// TODO : Create a notification
+
+		h.success("Response to the invitation was successfully saved!");
+	}
+
 	/**
 	 * Turn a GroupInfo object into a valid API object
 	 * 
diff --git a/src/controllers/Routes.ts b/src/controllers/Routes.ts
index bd765db..c7928fc 100644
--- a/src/controllers/Routes.ts
+++ b/src/controllers/Routes.ts
@@ -108,4 +108,6 @@ export const Routes : Route[] = [
 	{path: "/groups/get_members", cb: (h) => GroupsController.GetMembers(h)},
 
 	{path: "/groups/invite", cb: (h) => GroupsController.InviteUser(h)},
+
+	{path: "/groups/respond_invitation", cb: (h) => GroupsController.RespondInvitation(h)},
 ]
\ No newline at end of file
diff --git a/src/helpers/GroupsHelper.ts b/src/helpers/GroupsHelper.ts
index bb81afa..4dc3219 100644
--- a/src/helpers/GroupsHelper.ts
+++ b/src/helpers/GroupsHelper.ts
@@ -175,6 +175,37 @@ export class GroupsHelper {
 		}));
 	}
 
+	/**
+	 * Check if a user received an invitation to join a group or not
+	 * 
+	 * @param groupID Target group ID
+	 * @param userID Target user ID
+	 */
+	public static async ReceivedInvitation(groupID: number, userID: number) : Promise<boolean> {
+		return await DatabaseHelper.Count({
+			table: GROUPS_MEMBERS_TABLE,
+			where: {
+				groups_id: groupID,
+				user_ID: userID,
+				level: GroupMembershipLevels.INVITED
+			}
+		}) > 0;
+	}
+
+	/**
+	 * Respond to a membership invitation
+	 * 
+	 * @param groupID Target group ID
+	 * @param userID Target user ID
+	 * @param accept true to accept invitation / FALSE else
+	 */
+	public static async RespondInvitation(groupID: number, userID: number, accept: boolean) {
+		if(!accept)
+			await this.DeleteMember(groupID, userID);
+		else
+			await this.UpdateMembershipLevel(groupID, userID, GroupMembershipLevels.MEMBER);
+	}
+
 	/**
 	 * Insert a new group member
 	 * 
@@ -189,6 +220,39 @@ export class GroupsHelper {
 		});
 	}
 
+	/**
+	 * Update a user membership level
+	 * 
+	 * @param groupID Target group ID
+	 * @param userID Target user ID
+	 * @param level New membership level
+	 */
+	public static async UpdateMembershipLevel(groupID: number, userID: number, level: GroupMembershipLevels) {
+		await DatabaseHelper.UpdateRows({
+			table: GROUPS_MEMBERS_TABLE,
+			where: {
+				user_id: userID,
+				groups_id: groupID
+			},
+			set: {
+				level: level
+			}
+		});
+	}
+
+	/**
+	 * Delete completely a user membership
+	 * 
+	 * @param groupID Target group ID
+	 * @param userID Target user ID
+	 */
+	public static async DeleteMember(groupID: number, userID: number) {
+		await DatabaseHelper.DeleteRows(GROUPS_MEMBERS_TABLE, {
+			groups_id: groupID,
+			user_id: userID
+		});
+	}
+
 
 	/**
 	 * Get the membership level of a user for a group