For close to 40 years, cultural psychiatrists have struggled to institutionalize cross-cultural assessments with the recognition that culture influences ideas about desired and undesired treatments, social norms of appropriate and inappropriate communication in healthcare settings, and the ways that clinicians interpret symptoms into diagnoses. This chapter first establishes a common definition for the terms ‘culture’ and ‘migrant’, which can be used in mental health settings. Next, it traces how the care of migrants formed a central concern as psychiatrists, psychologists, and anthropologists made cultural recommendations for DSM-IV and DSM-5. Finally, the chapter discusses the DSM-5 Cultural Formulation Interview Supplementary Module for Immigrants and Refugees as a clinical assessment tool that can help clinicians ask patients about their backgrounds; pre-migration-, and post-migration trajectories; resettlement life; and plans for the future. This supplementary module may help clinicians systematically and comprehensively develop diagnostic assessments and treatment plans for immigrants and refugees in a patient-centred way.