This updated and expanded second edition brings together cutting-edge research across six continents to provide a comprehensive, global, up-to-date review of political uses of social media. In its 32 chapters, this second edition of the Routledge Companion to Social Media and Politics covers the good, the bad, and the as yet uncertain of current developments in the uses of social media in political contexts, ten years on from the first book. It is organised into six sections: Concepts, Challenges, Policies, Problems, Platforms, and Possibilities, each featuring chapters by leading researchers in the field that address these themes from a wide variety of viewpoints. This edition arrives at a new critical point: generative AI and other emerging technologies may either accelerate the crises of disinformation, polarisation, and democratic decline, or open new spaces for civic innovation, regulation, and accountability. The politics of digital platforms remain unsettled, and this Companion provides a critical map of the present while pointing to the possibilities and futures that will define the next decade of social media and politics. At a time when the politics of social media use remain unsettled, this comprehensive collection is an essential reference for academic communities in areas ranging from media and communication studies through internet studies and journalism studies to political science, and may be used by researchers as well as teachers and students in these respective fields. Chapters 3, 15 and 26 of this book are freely available as downloadable Open Access PDFs at http://www.taylorfrancis.com under a Creative Commons [Attribution-Non Commercial-No Derivatives (CC BY-NC-ND)] 4.0 International license.