A first step to implement effective migrant integration policies is to know who does what in policy sectors key to integration. Responding to this need, this paper offers policy makers a tool to understand the organisation of public action in key sectors for integration - Employment, Education, Housing, and Health/Welfare – in a sample of 10 OECD countries: Austria, Canada, France, Germany, Ireland, Italy, New Zealand, Spain, Sweden and the Netherlands. The complexity of the division of powers among levels of government calls for coordination mechanisms between actors, whatever the level of decentralisation. Besides, it throws lights on subnational governments’ role in integrating migrants and enabling them to participate to local development for the benefits of all. The geographic differences that exist in migrant presence and outcomes mean countries should build on local authorities' knowledge of local realities, aptitudes to coordinate different policy fields at the relevant scale and cooperate with non-governmental organisations.