This dissertation focuses on the communities occupying four of the chaotic online social spaces that millions of individuals enter, spend time in, and exit moment by moment—Anonymous, IGN.com, World of Warcraft, and Pirate Bay. Considering that political behavior occurs in all four explicitly non-political websites, I address the question of why only Anonymous and The Pirate Bay foster significant cross-national political mobilization. I argue that the construction of the technological space itself has a strong role in determining the possibility for political mobilization. In the four cases I analyze, three attributes of the technological space have been critical to mobilization: 1) the degree to which users identify themselves or remain anonymous, 2) the type of formal and informal regulation of the site, and 3) the degree to which the site provides opportunities for users to engage in small-group interaction. This argument is counter-intuitive: I demonstrate that the likelihood of political mobilization rises when a site provides high levels of anonymity, low levels of formal regulation, and minimal access to small-group interaction. In addition, I note in my observations of the four sites that a high level of conflict between the dominant norms in the online space and the legal and behavioral norms embraced offline provides a favorable context for political mobilization. This study shows that young people are more politically engaged than much of the literature on civic engagement suggests and that online mobilization may differ from traditional mobilization in that action arising from online social spaces appears to be more frequently episodic than sustained. The principal methodology I use for this study can be characterized as political ethnography. I use participant-observer and observational research methods; textual analysis of materials in community spaces; and process tracing, using news reports of behaviors, archived community documents and artifacts, and published interviews of prominent community members. The theoretical framing of this study draws on historical institutionalist work, theory about organizational culture, networked society theory, and comparative politics state-in-society approaches.