This article examines how the Internet transforms collective action. Current practices on the web bear witness to thriving collective action ranging from persuasive to confrontational, individual to collective, undertakings. Even more influential than direct calls for action is the indirect mobilizing influence of the Internet's powers of mass communication, which is boosted by an antiauthoritarian ideology on the web. Theoretically, collective action through the otherwise socially isolating computer is possible because people rely on internalized group memberships and social identities to achieve social involvement. Empirical evidence from an online survey among environmental activists and nonactivists confirms that online action is considered an equivalent alternative to offline action by activists and nonactivists alike. However, the Internet may slightly alter the motives underlying collective action and thereby alter the nature of collective action and social movements. Perhaps more fundamental is the reverse influence that successful collective action will have on the nature and function of the Internet.