diff --git a/STATUS.md b/STATUS.md
index f787742..bf77ee5 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -97,7 +97,7 @@ Implemented from [Client-Server API](https://matrix.org/docs/spec/client_server/
 
 - [x] [10.4.1 GET /_matrix/client/r0/joined_rooms](https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-joined-rooms)
 
-- [ ] [10.4.2.1 POST /_matrix/client/r0/rooms/{roomId}/invite](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-rooms-roomid-invite)
+- [ ] **[10.4.2.1 POST /_matrix/client/r0/rooms/{roomId}/invite](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-rooms-roomid-invite)**
 - [ ] [10.4.2.2 POST /_matrix/client/r0/rooms/{roomId}/join](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-rooms-roomid-join)
 - [ ] [10.4.2.3 POST /_matrix/client/r0/join/{roomIdOrAlias}](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-join-roomidoralias)
 
diff --git a/internal/backend.go b/internal/backend.go
index a89a7db..86a5431 100644
--- a/internal/backend.go
+++ b/internal/backend.go
@@ -49,4 +49,5 @@ type User interface {
 	Logout(token string)
 	LogoutAll()
 	JoinRoom(Room) models.ApiError
+	Invite(Room, User) models.ApiError
 }
diff --git a/internal/backends/memory/rooms.go b/internal/backends/memory/rooms.go
index 7131f37..63c5057 100644
--- a/internal/backends/memory/rooms.go
+++ b/internal/backends/memory/rooms.go
@@ -21,6 +21,7 @@ type Room struct {
 
 	creator internal.User
 	joined  []internal.User
+	invites []internal.User
 
 	events []RoomEvent
 
diff --git a/internal/backends/memory/user.go b/internal/backends/memory/user.go
index 9766654..4a2e90f 100644
--- a/internal/backends/memory/user.go
+++ b/internal/backends/memory/user.go
@@ -122,6 +122,42 @@ func (user *User) SetTopic(room internal.Room, topic string) models.ApiError {
 	return nil
 }
 
+func (user *User) Invite(room internal.Room, invitee internal.User) models.ApiError {
+	memRoom := room.(*Room)
+
+	memRoom.mutex.Lock()
+	defer memRoom.mutex.Unlock()
+
+	userInRoom := false
+
+	for _, roomUser := range memRoom.joined {
+		if user.ID() == roomUser.ID() {
+			userInRoom = true
+		}
+	}
+
+	if !userInRoom {
+		return models.NewError(models.M_FORBIDDEN, "the inviter is not currently in the room") // TODO: check code
+	}
+
+	// TODO: remove repeated cycle
+	for _, roomUser := range memRoom.joined {
+		if roomUser.ID() == invitee.ID() {
+			return models.NewError(models.M_FORBIDDEN, "the invitee is already a member of the room.") // TODO: check code
+		}
+	}
+
+	for _, inviteeUser := range memRoom.invites {
+		if inviteeUser.ID() == invitee.ID() {
+			return models.NewError(models.M_FORBIDDEN, "user already has been invited") // TODO: check code
+		}
+	}
+
+	memRoom.invites = append(memRoom.invites, invitee) // TODO: add invite event + info about inviter
+
+	return nil
+}
+
 func (user *User) LeaveRoom(room internal.Room) models.ApiError {
 	room.(*Room).mutex.Lock()
 	defer room.(*Room).mutex.Unlock()
diff --git a/internal/backends/memory/user_test.go b/internal/backends/memory/user_test.go
index 27ac421..55026aa 100644
--- a/internal/backends/memory/user_test.go
+++ b/internal/backends/memory/user_test.go
@@ -192,3 +192,25 @@ func TestLogoutAll(t *testing.T) {
 
 	assert.Len(t, user.Devices(), 0)
 }
+
+func TestInviteUser(t *testing.T) {
+	backend := NewBackend("localhost")
+
+	user1, _, err := backend.Register("username1", "", "")
+	assert.NoError(t, err)
+
+	user2, _, err := backend.Register("username2", "", "")
+	assert.NoError(t, err)
+
+	request := createroom.Request{
+		RoomAliasName: "room1",
+		Name:          "room1"}
+
+	room, err := user1.CreateRoom(request)
+	assert.NoError(t, err)
+	assert.Len(t, room.(*Room).invites, 0)
+
+	err = user1.Invite(room, user2)
+	assert.NoError(t, err)
+	assert.Len(t, room.(*Room).invites, 1)
+}