Mobile, migrant and displaced people require specific attention with regard to HIV vulnerability, including information and services tailored to their social, cultural and economic backgrounds and to the phase of mobility. Too few studies have systematically documented the needs of people on the move in this regard or evaluated the existing responses to meeting these needs. Most studies and programme descriptions focus on specific populations at country or community levels. Few compare and contrast different population groups, and few are regional or cross-continental in scope. Most are purely descriptive, and lack a theoretical framework. The aim of this article is to precipitate more structured international comparisons – and questions – that will fill some of the evidence and programming gaps defined.