ABSTRACTBecause HIV and AIDS key populations share common social-cultural factors challenging their sexual health and rights (e.g. stigma, criminalisation), there is an assumed benefit of collaborative programmes where various key populations work in solidarity. In this paper, we reflect on how partners collaborated in a complex alliance of over 100 different NGOs, representing and supporting three key populations – lesbian, gay, bisexual and transgender (LGBT) people, sex workers and people who use drugs – working across 16 countries. We used a multiple-method approach of participant observation, qualitative interviews, and a survey to explore the benefits, facilitators and challenges of collaboration. Results show that motivators for collaboration included being part of the larger funding structure with applied impacts, a repressive human rights context, and intersectionality. Barriers for collaboration included identity politics, stigma, and constraints regarding the appropriate timing of new collaborations. Finally, facilitators include practical support for engagement, the framing of human rights in a medical agenda, and recognition of implicit differences. We conclude that for building the capacity for collaboration among socially marginalised groups it is important to develop trust and the ability to recognise strength in difference beyond the initial identification of shared norms and common goals.