diff --git a/client.go b/client.go
index f68cae63..e7cafe4f 100644
--- a/client.go
+++ b/client.go
@@ -978,6 +978,22 @@ func (cli *Client) GetProfile(ctx context.Context, mxid id.UserID) (resp *RespUs
 	return
 }
 
+func (cli *Client) GetMutualRooms(ctx context.Context, otherUserID id.UserID, extras ...ReqMutualRooms) (resp *RespMutualRooms, err error) {
+	if cli.SpecVersions != nil && !cli.SpecVersions.Supports(FeatureMutualRooms) {
+		err = fmt.Errorf("server does not support fetching mutual rooms")
+		return
+	}
+	query := map[string]string{
+		"user_id": otherUserID.String(),
+	}
+	if len(extras) > 0 {
+		query["from"] = extras[0].From
+	}
+	urlPath := cli.BuildURLWithQuery(ClientURLPath{"unstable", "uk.half-shot.msc2666", "user", "mutual_rooms"}, query)
+	_, err = cli.MakeRequest(ctx, http.MethodGet, urlPath, nil, &resp)
+	return
+}
+
 // GetDisplayName returns the display name of the user with the specified MXID. See https://spec.matrix.org/v1.2/client-server-api/#get_matrixclientv3profileuseriddisplayname
 func (cli *Client) GetDisplayName(ctx context.Context, mxid id.UserID) (resp *RespUserDisplayName, err error) {
 	urlPath := cli.BuildClientURL("v3", "profile", mxid, "displayname")
diff --git a/requests.go b/requests.go
index 595f1212..5611bd57 100644
--- a/requests.go
+++ b/requests.go
@@ -140,6 +140,10 @@ type ReqMembers struct {
 	NotMembership event.Membership `json:"not_membership,omitempty"`
 }
 
+type ReqMutualRooms struct {
+	From string `json:"-"`
+}
+
 // ReqInvite3PID is the JSON request for https://spec.matrix.org/v1.2/client-server-api/#post_matrixclientv3roomsroomidinvite-1
 // It is also a JSON object used in https://spec.matrix.org/v1.2/client-server-api/#post_matrixclientv3createroom
 type ReqInvite3PID struct {
diff --git a/responses.go b/responses.go
index 26aaac77..6ead355e 100644
--- a/responses.go
+++ b/responses.go
@@ -159,6 +159,11 @@ type RespUserProfile struct {
 	AvatarURL   id.ContentURI `json:"avatar_url"`
 }
 
+type RespMutualRooms struct {
+	Joined    []id.RoomID `json:"joined"`
+	NextBatch string      `json:"next_batch,omitempty"`
+}
+
 // RespRegisterAvailable is the JSON response for https://spec.matrix.org/v1.4/client-server-api/#get_matrixclientv3registeravailable
 type RespRegisterAvailable struct {
 	Available bool `json:"available"`
diff --git a/versions.go b/versions.go
index 672018ff..5c0d6eaa 100644
--- a/versions.go
+++ b/versions.go
@@ -63,6 +63,7 @@ var (
 	FeatureAsyncUploads       = UnstableFeature{UnstableFlag: "fi.mau.msc2246.stable", SpecVersion: SpecV17}
 	FeatureAppservicePing     = UnstableFeature{UnstableFlag: "fi.mau.msc2659.stable", SpecVersion: SpecV17}
 	FeatureAuthenticatedMedia = UnstableFeature{UnstableFlag: "org.matrix.msc3916.stable", SpecVersion: SpecV111}
+	FeatureMutualRooms        = UnstableFeature{UnstableFlag: "uk.half-shot.msc2666.query_mutual_rooms"}
 
 	BeeperFeatureHungry               = UnstableFeature{UnstableFlag: "com.beeper.hungry"}
 	BeeperFeatureBatchSending         = UnstableFeature{UnstableFlag: "com.beeper.batch_sending"}