This special issue explores the role of social movements in bringing about, or failing to bring about, political and social transformation. We have included articles that examine this topic broadly, from a wide range of perspectives with psychology as a central theme. The focus includes the relationship among social movements, radicalization, and nonviolence or violence. And most particularly, this Special Issue explores the bidirectional association between social movements and what Galtung (1969) has called direct, cultural, and structural violence. In this Introduction, we review the questions of interest and the broad aims of the Special Issue, as well as the role of each selected article, and key achievements and limitations.