The role of the internet in radicalizing individuals to extremist action is much discussed but remains conceptually and empirically unclear. Here we consider right-wing and jihadist use of the Internet – who posts what and where. We focus on extremist content related to radicalization to violent action, and argue that victim videos and jihad videos are particularly powerful in moving individuals to radical action. We interpret these two kinds of video as complementary parts of the kind of mobilization frame studied by social movement theorists. Finally we consider various kinds of government effort to control extremist content on the Internet.