In economic studies of the private rental sector of the housing market, and in political debates on housing policy, it is often assumed that private landlords are basically guided by rational economic motives. In this paper, which is based on a Danish study of housing rehabilitati on activity among private landlords under rent control, it is shown that differen t groups of landlords exist who have many other motives for buying and maintaining rental property than those assumed in economic theory. It is concluded that private landlords do not behave as economic, rational and ef® cient actors as is often assumed, and that an understanding of these structures of landlordism is essential to an assessment of the role of private landlords in housing supply, and to an elaboration of public programmes for supporting housing rehabilitat ion in the private rental sector.