People use online social forums for all sorts of reasons, including political conversations, regardless of the site's main purpose. But what leads some of these people to take their online political activity into the offline world of activism? In Expect Us, Jessica L. Beyer looks at political consciousness and action in four communities, each born out of chaotic online social spaces that millions of individuals enter, spend time in, and exit moment by moment: Anonymous (4chan), IGN, World of Warcraft, and The Pirate Bay. None of these sites began as places for political organization per se, but visitors to each have used them as places for political engagement to one degree or another. Beyer explains the puzzling emergence of political engagement in these disparate social spaces and offers reasons for their varied capacity to generate political activism. Her comparative ethnography of these four online communities demonstrates that the technological organization of space itself has a strong role in determining the possibility of political mobilization. Overall, she shows that political mobilization rises when a site provides high levels of anonymity, low levels of formal regulation, and minimal access to small-group interaction. Furthermore, her findings reveal that young people are more politically involved than much of the civic engagement literature suggests. Expect Us offers surprising and compelling insights for anyone interested in understanding which factors and online environments lead to the greatest amount of impact offline.