This book provides a comprehensive overview of the manifestations and interrelations of collectivity and power on the internet from a sociological point of view. It addresses questions on how different forms of internet-based collectivities (masses, crowds, movements, communities) can be understood and differentiated from one another. It presents analyses on the role technical infrastructures of the web play in their formation, how the mobilization and organization of social movements and protests have changed through social media, how work and decision-making processes are organized in open source communities, and why the essential segments of the commercial internet are today concentrated in the hands of a few corporations that hold significant economic, infrastructural, and rule-setting power.