This article seeks to reconcile the activities of several of the groups organized during the 2004 election cycle under section 527 of the Internal Revenue Code with existing theories of party and interest group behavior. While 527 groups have frequently been categorized as extensions of traditional advocacy groups or party networks, I argue that existing theories do not account for the functional differentiation between these groups. This functional differentiation marks a relatively unprecedented development in American interest group politics. However, the highly partisan nature of the 2004 election and the limited appeal of these groups either to party donors or to a broad base of interest groups may indicate that such groups will not endure or play as prominent a role in 2008 as they did in 2004 even absent changes in FEC rules.