In much of the literature on HIV/AIDS and mobility, mobile populations and/or migrants are described and treated as one, homogenous group. This report from the International Organisation for Migration examines the different sub-groups of mobile populations, and looks at their commonalities and differences. The report notes that mobile groups are vulnerable to HIV/AIDS in different respects, which complicates prevention and mitigation strategies. Vulnerability to HIV/AIDS is often related to a particular stage of the mobility process.