Variations in definitions used for "migrant" and for different groups of migrants in different areas can affect health systems' policies and migrants' access to health care. This systematic review explored this issue using evidence from academic peer-reviewed and grey literature in 169 publications in English or Russian from 2010 to 2015 that focused on primary care or both primary and secondary care, including screening services and emergency departments. There is no universally accepted definition for migrant at an international level and the heterogeneity of the definitions used limits the comparability of routinely collected data. Legal status was one of the most significant factors determining access to affordable and adequate health services for migrants in a country. This publication recommends as policy options: identifying preferred terms for migrants, seeking consensus on important migration-related variables for collection across health information systems and progressing towards universal access to health care across the WHO European Region.