The number of people on the move internationally is increasing, and a sizable number of these individuals are migrating through and to the WHO European Region. The UN Sustainable Development Goals demand that we leave no one behind and ensure equitable implementation of Universal Health Coverage (UHC), regardless of immigration status. In the WHO European region, some of the migrants in the most precarious situations are undocumented; defined as those who may have been unsuccessful in asylum applications, born to undocumented parents, continued their residence in a country after their permit or other means of stay expired, as well as those who have entered the country irregularly. These undocumented migrants face some of the biggest challenges to accessing UHC and are often left behind by systems that exclude and stigmatise them. This paper examines the literature on access to healthcare for undocumented migrants in the WHO European Region and calls for urgent action towards ensuring UHC for all migrants regardless of immigration status by 2030.