This article provides a critical comparative analysis of mobile versus personal computer (PC)-based forms of Internet access. Drawing from an interdisciplinary body of literature, it illustrates a wide range of ways in which mobile Internet access offers lower levels of functionality and content availability; operates on less open and flexible platforms; and contributes to diminished levels of user engagement, content creation, and information seeking. At a time when a growing proportion of the online population is “mobile only,” these disparities have created what is termed here a mobile Internet underclass. The implications of this argument for digital divide policymaking and, more broadly, for the evolutionary trajectory of the Internet and the dynamics of Internet usage are discussed.