Leftwing activism of recent decades exhibits an anarchist turn evident in quantitative indicators like mentions of anarchists in news reports and by activists adopting anarchist modes of organization, tactics, and social goals-whether or not they claim that label. The authors of this Element argue that the very crises that generated radical mobilizations since the turn of the millennium have both led activists to reject other strategies for social transformation and to see anarchist practices as appropriate to the challenges of our time. This turn is clearly apparent in the Americas and Europe, and has reverberations on an even broader transnational, perhaps global, scale. This suggests the need for research on social movements to consider anarchists and other marginalized radical traditions more fully, not just as objects of study, but as important sources of theory.