A set of collaborative contacts may be selected with an invitation user interface. An invitation to participate in a collaborative activity may be sent to the selected contacts from the invitation user interface or from a collaborative application. The invitation may be received by a collaborative services platform. A user of the collaborative services platform may be presented with the invitation along with an ability to choose one of accept, decline and ignore in response to the invitation. The user may choose to accept, decline or explicitly ignore the invitation, and a response may be sent to the sender of the invitation indicating the user's choice. An application programming interface for a collaborative invitation service of the collaborative services platform may include an invitation element, a send invitation element, a respond to invitation element and a cancel invitation element. The cancel invitation element may be used to cancel issued invitations.