In Windows Live Messenger, two users can chat with each other only if they have a contact relationship. When they become contacts, they also learn each other's e-mail addresses.

In many social applications, users want to see the presence of other users and chat with them even if they do not know each other. For example, on a video-sharing site, a user may want to send an instant message to the creator of a video, but may not want to make that user a contact or share e-mail addresses.

With the Windows Live Messenger Web Toolkit, users who link their Messenger accounts with an application can chat with one another without becoming Messenger contacts. You can write your application to enable this functionality with application contacts. By making user A an application contact of user B, that application can enable users A and B, who are not on each other's Messenger contact list, to see each other's presence and send instant messages to one another.

With application contacts, an application can also show user profile data, such as name and display picture, regardless of whether the site visitor is signed in with the Messenger Web Toolkit.

An application contact must be a Windows Live user whose account is linked with the application.