The idea that most poor people live in their own self-help house is inaccurate insofar as large of poor people in the Third World cities rent their home. The most likely explanation for this bias is that the growth of irregular settlements has been so pronounced that it has dominated perceptions of the housing problems. The article deals with several questions about rental housing, mainly: who are the renters? how is the rental market organized? what determines the size the rental housing market? and mobility of housing households. The analysis is based on studies on Mexico and Columbia, as well as of the presently avalaible literature.