In the context of shifting regulatory approaches and changing provision structures in many Western rental housing systems, the notion of competition between social and private rental housing has received increasing attention from practitioners and academic researchers. This thesis explores and theorises the concept of inter-tenure competition in order to advance understanding of what it means in local and national market realities, as well as in business and political practices. Results indicate that competition in mixed markets is a complex matter, much of which is explained by the distinctive properties of social and private rental services. Inter-tenure competition is shown to be the interplay of structural and political conditions, individual and organisational business goals, and the perceptions and strategic decisions of both providers and consumers. The results suggest that the degree of competition relates to specific points in time and is mainly a question of which rental market segment one is looking at.