Activists are people who actively work for social or political causes and especially those who work to encourage other people to support those causes. Mass collective action is unlikely to occur without the involvement of activists. Including recent research from Australia, Europe, and North and South America, and studies of global online activists, this issue highlights multi-method approaches to studying activists and activism across a variety of different regional, issue-based, and socio-political contexts. In addition to contributing to ongoing theoretical and empirical discussions, the issue addresses the policy and strategic implications of this research for social change agents and organizations.