Book excerpt: In less than a decade, a new breed of progressive media projects have captured huge, non-traditional audiences and shaped political campaigns, public debates and policy in ways that could never have been imagined in a previous era. Drawing on years of research, media experts Jessica Clark and Tracy Van Slyke now lay out a clear, hard-hitting theory of media impact. Their study showcases influential projects such as TPM Caf , FireDogLake and Feministing, suggesting ways in which media makers can exploit changes in journalism, technology, and politics.