What political power do videos on social media have? In what ways do they exert influence, shape publics and change political life? And how can committed civil society actors in this field assert themselves against hegemonic discourses, commercial interests, anti-democratic agitation, and authoritarian propaganda? These questions are being debated intensely as social media increasingly dominate global information flows, and videos increasingly dominate social media. Understanding video activism seems particularly relevant at a time when the internet is undergoing fundamental disruptions. The forms, practices, and opportunities of activism depend on its media environment, which now is changing rapidly and profoundly in terms of its technological basis, ownership, legal regulations, and governmental control.