A key element of sustainable development in cities is the implementation of more effective, less polluting, and equitable transportation policy. This article examines the role of activist organizations promoting transport alternatives in London, Britain's capital city and its largest metropolitan area. Major national, citywide, and local policy changes have permitted citizens' groups to work more actively with progressive elements in government planning, breaking down citizen-expert divides. In West London, the most congested sector of the metropolis, an environmentally based social network, the Ealing Cycling Campaign, promotes cycling as a sustain-able transport alternative. Its strategies require active cooperation with the local state rather than radical opposition to it, raising questions about the oppositional stance more commonly found among urban social movements. Environmental citizenship needs to be founded on social realities and conduced in mainstream political systems if it is to be effective in complex urban environments.