How are nonprofit organizations utilizing social media to engage in advocacy work? We address this question by investigating the social media use of 188 501(c)(3) advocacy organizations. After briefly examining the types of social media technologies employed, we turn to an in-depth examination of the organizations’ use of Twitter. This in-depth message-level analysis is twofold: A content analysis that examines the prevalence of previously identified communicative and advocacy constructs in nonprofits’ social media messages; and an inductive analysis that explores the unique features and dynamics of social media-based advocacy and identifies new organizational practices and forms of communication heretofore unseen in the literature.