This book undertakes research at the intersection of social media and protest. Far from being neutral platforms, social media possess their own material characteristics, which shape how people engage, protest, resist, and struggle. We advance the notion of social media materialities to draw attention to the ways in which the wires and silicon, data streams and algorithms, user and programming interfaces, business models and terms of service steer contentious practices and, inversely, how technologies and economic models are handled and performed by users. Scholars have long studied media as tools taken up by activists and other social actors or as inherently political determinants. Especially with the emergence of social media platforms such as Twitter, Facebook, Instagram, Snapchat, Weibo, and YouTube, scholars have focussed either on the benefits for activists, such as accelerated processes of political mobilization, or on the drawbacks in terms of control and surveillance (for an overview, see Chapter 8 of this volume; Neumayer & Svensson 2016; Poell & van Dijck 2018).