David Karpf is the author of The MoveOn Effect: The Unexpected Transformation of American Political Advocacy (Oxford University Press 2012) and an assistant professor in the School of Media and Public Affairs at George Washington University. His book is timely, well-researched, and insightful. He explores the adoption of Internet technologies by advocacy groups in the early 2000s, specifically MoveOn, DailyKos, and Democracy for America. Karpf argues that these technologies are transformative and disruptive, permitting the establishment of whole new types of advocacy group based on low-cost, high-speed virtual mobilization and organizing. Readers from both the academic and professional political world would benefit from reading this book. Its conclusions suggest a radical change in the population of interest groups as we know it.