The provision of urban public mass transportation in Latin America has exhibited marked swings during the last century. Various cities have experimented with public and private provision, as well as different types of market regulation ranging from almost total liberalization to intervention in fares, route allocations, bus size, service quality, and exclusive road lanes. Despite the importance of this sector for the quality of social life and urban economic development, the literature contains little theoretical research on the market failures characteristic of this industry. There are also few studies on the consequences of alternative provision and regulation arrangements. This paper contributes to this second area of research. We describe the experience of Bogotá, Colombia, where a new hybrid system of urban public transport was put in place at the beginning of this century---hence its name, TransMilenio. The new system was designed after decades of learning about the failures of both publicly and privately owned systems. It currently supplies more than 20 percent of daily trips. By 2015, the complete TransMilenio system is expected to transport 80 percent of the city's population at an average speed of 25 kilometers per hour with a service quality similar to an underground metro system.