A new anthology celebrating the accomplishments of the Critical Mass movement over the past twenty years. From both theoretical and practical perspectives, the book explores how Critical Mass has gone around the world, how it has evolved along the way, and the impacts it has had on local politics, transportation, and cultures. Critical Mass was born 20 years ago among dozens of people in San Francisco and has reproduced itself in over 350 cities around the world thanks to the diligent efforts of countless thousands across the planet. Often just a few people start riding together and it attracts others to join, gaining momentum steadily until it bursts onto a city’s political and social landscape. Moreover, the concept of riding together en masse is open-ended enough that people have adapted it in many ways during the past decades, from altering the structure of formal recreational riding to using “Critical Mass-style” rides to bring attention to a wide range of political campaigns and issues.