Ireland experienced dramatic political, social and economic change in the twentieth century, of which the shift from a majority rural to a majority urban population was one of the most notable. These changes are refl ected in the nature and form of the built environment. In this essay, the evolution of urban and suburban housing during Ireland’s first urban century is considered. Existing patterns of unplanned middleclass suburban expansion were supplemented, from the 1920s, by a programme of planned working-class suburbanization. State intervention thus impacted on the location and form of new housing estates, while layouts owed much to the early British town-planning movement. High levels of owner-occupation in Ireland, the combined result of government policy and individual preference, were also reflected in a preference for particular housing forms. The predominance of the standardised three- or four-bedroom, semi-detached or detached house, was not challenged until the 1990s when there was a surge in apartment provision, largely driven by tax incentives. Changing norms in terms of housing size, facilities and design were shaped by the standards adopted by government and local authorities, as well as to the pressures of the speculative building process.