This article examines the policy and practice of spatial planning in the Dublin city region over the period from 1990 to 2006. This period has been characterized by rapid demographic and economic expansion and increased dispersal of urban and peri-urban development across a spatially extensive functional urban region. Spatial planning policy and practice at local, regional and national scales has sought to steer the spatial distribution of urban development in accordance with broad policy principles of sustainable development and balanced regional development. This article critically examines the governance capacity of regional-scale spatial planning strategies to manage urban expansion in a dynamic market-led development context and finds in this case a significant absence of conformance between strategic objectives and spatial development outcomes.