The outbreak of the First World War in 1914 saw the introduction of more interventionist housing policy measures in the UK with legislation that introduced rent controls. Subsidies to encourage local authorities to build new housing was the other key policy that affected patterns of residential building across the UK and changed tenure patterns in the inter-war years, until 1939. The expansion of owner occupation was also evident in this period and associated with the role of building societies. The Chapter discusses contested views about the reasons for the introduction and retention of rent controls and for the decline of private landlordism, alongside the expansion of owner occupation. Uneven geographical patterns of council house building were affected by periodic changes to housing subsidies and by other factors and subsidy arrangements also largely explain why council housing developed to house securely employed, affluent working class families rather than a cross section of the population.