Increasingly, the search for sustainable transport has reflected the awareness that cycling, walking and the liveable cities that encourage these activities lie at the centre of any effective strategy. While citizens' groups are often encouraged, instructed or expected to support these initiatives, to date, there have been few studies of how these citizens' groups work. This article examines how a partnership between Living City (Ciudad Viva), a community-based organization; Interface for Cycling Expertise, a Dutch non-governmental organization; and Metropolitan Santiago's regional government applied collaborative planning and other methods to build effective processes for more cycling-inclusive transport policies in Santiago, Chile. The resulting actors' ecologies mobilized substantial knowledge and goodwill. After just three years, cycling had become a presidential priority, cycling infrastructure design skills had improved substantially, and both politicians and citizens had made significant commitments to more cycling- and walking-friendly urban environments. This study provides insights into the nuts and bolts of how some civil society organizations develop, what they can contribute to sustainable transport and what environments and support they need to be effective.