The integration of refugees and other vulnerable migrants in the host countries is essential to foster social cohesion and promote the economic benefits of migration. OECD countries were taken by surprise by the recent increase in inflows of humanitarian migrants. The refugee population in OECD countries tripled in just four years, between 2013 and 2017. But in addition to the recent upsurge in refugees, there have also been an increasing number of migrants admitted to OECD countries on other grounds; many of them face similar vulnerabilities and challenges in integrating in the host country. The humanitarian crisis raised many challenges to the host countries, but reception systems largely managed the strain of coping with sudden, large and unexpected inflows of people seeking protection. Record inflows, however, leave a legacy of increased demand for integration. Successful integration is as much a challenge as providing initial reception. Failure on this front would carry significant economic and social costs, constrain future policy-making and weaken trust in government.