Students of social movements have long been fascinated by the ways in which they influence or spread from one site to another – in short, how they diffuse. Recent scholarship has shed light on different dimensions of the diffusion process, including the actors, networks, and mechanisms that make diffusion happen. This volume is an attempt to pull together different strands of this research into an integrated and comprehensive understanding of the diffusion process.

Most of the contributors to this volume participated in a conference at Cornell University in November 2007 that explored how social movements create linkages and frame issues under contention. The conference was an initiative of an interdisciplinary theme project, “Contentious Knowledge: Science, Social Science, and Social Protest,” sponsored by Cornell's Institute for the Social Sciences. This project brought together scholars who study contentious politics with others who explore the social construction (and contestation) of authoritative knowledge. The dialogue among these scholars sparked considerable interest in the diffusion of mobilizing tactics and frames across activist networks. It also revealed the need for a single volume to integrate what we know about the diffusion of social movements and identify some of the new research frontiers on the topic. We hope this volume contributes to these goals.