This paper uses travel survey data to explore the social dimension of urban travel in Nairobi. It seeks to explain why, where and how people in Nairobi travel and the implications of that behavior pattern. The paper has two parts: an in-depth exploration of the travel patterns and preferences of Nairobi residents and a discussion of the implications of these results for transport policy in this city. The data show that the lack of suitable transport infrastructure exacerbates travel challenges for residents across all income groups. A substantial portion of the local population cannot regularly afford any form of motorized transportation. They thus are forced to locate in slums near sources of employment, and the widespread lack of pedestrian and bicycle infrastructure increases the risk that they face when travelling. The middle income group who cannot afford private cars is almost completely dependent on the public transport system. Any disruption in the public transport service severely disrupts their lives and their livelihoods. For the privileged 15-20 percent of Nairobi households who own cars, they are at the mercy of the congested, under-maintained, and dangerous roadways. Finally, as in most other parts of the world, it is clear that once a Nairobi resident owns a car, s/he is going to use it for as many of his or her transportation needs as possible. Unless public transport can be removed from the traffic congestion so that travelling is substantially faster by public transport than by private car, very few car owners will be using the system.