diff --git a/README.md b/README.md
index 1acd7cc..ec680f9 100644
--- a/README.md
+++ b/README.md
@@ -13,3 +13,4 @@ Implemented from [Client-Server API](https://matrix.org/docs/spec/client_server/
 - [x] [5.4.1 GET /_matrix/client/r0/login](https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-login)
 - [x] [5.4.2 POST /_matrix/client/r0/login](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-login)
 - [x] [5.4.3 POST /_matrix/client/r0/logout](https://matrix.org/docs/spec/client_server/latest#post-matrix-client-r0-logout)
+- [x] [5.7.1 GET /_matrix/client/r0/account/whoami](https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-account-whoami)
\ No newline at end of file
diff --git a/internal/backend.go b/internal/backend.go
index e4136df..0e8dbe0 100644
--- a/internal/backend.go
+++ b/internal/backend.go
@@ -11,6 +11,7 @@ type Backend interface {
 	Register(username, password, device string) (user User, token string, err *models.ApiError)
 	Login(username, password, device string) (token string, err *models.ApiError)
 	Logout(token string) *models.ApiError
+	GetUserByToken(token string) (user User)
 	Sync(token string, request sync.SyncRequest) (response *sync.SyncReply, err *models.ApiError)
 }
 
diff --git a/internal/backends/memory/backend.go b/internal/backends/memory/backend.go
index 0a160e9..97a5cb1 100644
--- a/internal/backends/memory/backend.go
+++ b/internal/backends/memory/backend.go
@@ -91,3 +91,18 @@ func (backend *Backend) Sync(token string, request mSync.SyncRequest) (response
 
 	return nil, nil // TODO: implement
 }
+
+func (backend *Backend) GetUserByToken(token string) internal.User {
+	backend.mutex.Lock()
+	defer backend.mutex.Unlock()
+
+	for _, user := range backend.data {
+		for userToken := range user.(*User).Tokens {
+			if userToken == token {
+				return user
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/internal/handlers.go b/internal/handlers.go
index 7ed24a4..2872685 100644
--- a/internal/handlers.go
+++ b/internal/handlers.go
@@ -15,6 +15,7 @@ import (
 	register "github.com/nxshock/signaller/internal/models/register"
 	mSync "github.com/nxshock/signaller/internal/models/sync"
 	"github.com/nxshock/signaller/internal/models/versions"
+	"github.com/nxshock/signaller/internal/models/whoami"
 )
 
 func RootHandler(w http.ResponseWriter, r *http.Request) {
@@ -126,6 +127,20 @@ func RegisterHandler(w http.ResponseWriter, r *http.Request) {
 	sendJsonResponse(w, http.StatusOK, response)
 }
 
+// https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-account-whoami
+func WhoAmIHandler(w http.ResponseWriter, r *http.Request) {
+	token := getTokenFromResponse(r)
+	if token == "" {
+		errorResponse(w, models.M_FORBIDDEN, http.StatusForbidden, "")
+	}
+
+	user := currServer.Backend.GetUserByToken(token)
+
+	response := whoami.Response{UserID: user.ID()}
+
+	sendJsonResponse(w, http.StatusOK, response)
+}
+
 // https://models.org/docs/spec/client_server/latest#get-models-client-r0-sync
 func SyncHandler(w http.ResponseWriter, r *http.Request) {
 	var request mSync.SyncRequest
diff --git a/internal/models/whoami/whoami.go b/internal/models/whoami/whoami.go
new file mode 100644
index 0000000..db228c4
--- /dev/null
+++ b/internal/models/whoami/whoami.go
@@ -0,0 +1,6 @@
+package whoami
+
+// https://matrix.org/docs/spec/client_server/latest#get-matrix-client-r0-account-whoami
+type Response struct {
+	UserID string `json:"user_id"` // Required. The user id that owns the access token.
+}
diff --git a/internal/server.go b/internal/server.go
index e3e4c22..3f208de 100644
--- a/internal/server.go
+++ b/internal/server.go
@@ -22,6 +22,7 @@ func New() *Server {
 	router.HandleFunc("/_matrix/client/r0/login", LoginHandler)
 	router.HandleFunc("/_matrix/client/r0/logout", LogoutHandler)
 	router.HandleFunc("/_matrix/client/r0/register", RegisterHandler)
+	router.HandleFunc("/_matrix/client/r0/account/whoami", WhoAmIHandler)
 	router.HandleFunc("/_matrix/client/r0/sync", SyncHandler)
 	router.HandleFunc("/", RootHandler)