This chapter introduces the key debates about critical security studies and social media that will frame the discussions in the rest of this book. Key in this is challenging simplistic and unidirectional assumptions about social media and its role in the sphere of politics and security. To do this, this introduction sets out three key assumptions that underpin the rest of this book. The first takes up the call within critical security studies to shatter disciplinary boundaries when we examine security in the unregulated space of social media. Secondly, related to this expansion of disciplines, scholars need to “expect the unexpected” when examining security on social media as the range of idioms, symbols, narratives and ideas used to re-frame, subvert and contest security on social media is breath-taking. Thirdly, scholars also need to be aware of the fickle nature of social media, and the constantly changeable nature of platforms, data sources and locations of security on social media which requires significant and ongoing methods and methodological innovations. Fourthly, the emancipatory burden of critical theory, and by extension critical security studies, weighs heavily also on broader discussions of social media’s political potential. The results are extremely mixed, with social media being enmeshed in relations of control, commodification and emancipation. This book argues that social media offers only a “thin” form of discursive emancipation, where it gives previously unheard voices a platform, but the potential of this to change power relations in the “real world” are unclear.