Social-networking websites let users build socialconnections with family, friends, and coworkers. Users can also build profiles for storingand sharing various types of content withothers, including photos, videos, and messages. Updating user profiles with interesting content is aform of self-expression that increases interaction in suchsites. To encourage this interaction and provide richer content, social-networking sites expose their networks to Webservices in the form of online application programminginterfaces. These APIs allow third-party developers tointerface with the social-networking site, access information and media posted with user profiles, and build socialapplications that aggregate, process, and create contentbased on users’ interests.Social-networking sites provide numerous application services that can mash up user-profile data withthird-party data. In addition, third-party sites can rapidlydistribute their services via social-networking sites to keepin touch with users while they’re on these sites. Moreover,users can enjoy various applications with content fromnumerous third-party sites: users access social-networkingsites, where they maintain their profiles; third-party sitesretrieve these profiles, enrich the content, and return themto the social-networking sites for consumption by the userand, possibly, friends. For example, Facebook users canshare music with friends, create playlists, and get concertalerts on their profile page by installing the third-partymusic application iLike (www.ilike.com).Major social-networking sites have begun launchingsocial-networks connect services such as Facebook Platform, Google Friend Connect, and MySpaceID that furtherbreak down the garden walls of social-networking sites.These SNCSs let third-party sites develop social applications and extend their services without having to eitherhost or build their own social network. This extensionallows third-party sites to leverage the social-networkingsite’s features.For example, third-party sites can exploit the authentication services provided by a social-networking site so thatusers need not create another username and passwordto access the third-party site; instead, users can draw ontheir social-network credentials and established profile.Users can also access third-party sites that leverage socialnetwork user-profile content. The third-party sites retrieveusers’ profiles from the social-networking site to createan enhanced experience. In this way, they can increasemembership by providing more interesting content froma variety of sources in a seamless manner.