Men who have sex with men (MSM) remain the group with the highest incidence of HIV in the UK, with a high concentration of infections in London. Multi-site safety and efficacy trials have demonstrated significant reductions in HIV acquisition among MSM when prescribed a daily pre-exposure prophylaxis (PrEP). Success translating these scientific developments into effective prevention interventions requires an understanding of how acceptable they are to individuals at risk of HIV acquisition. This thesis reports on the findings of twenty in-depth semi-structured qualitative interviews with MSM in London. To participate, men must have had at least one episode of sex without condoms with a known sero-discordant partner or a partner of unknown HIV status in the twelve months prior to interview. The acceptability of a range of PrEP methods were explored, including daily and intermittent oral; topical; and injectable formulations of PrEP and the potential impact of PrEP use upon men’s perceptions of risk and behaviours. Dimensions of acceptability draw on the personal (such as side effects; increased or diminished HIV vulnerability; adherence to drug/medical regimes); the inter-personal (such as negotiation of sex; stigma or discrimination); and community or social concepts of acceptability (such as financial burden and concepts of increased ‘community risk’). The thesis provides a framework for understanding PrEP acceptability, showing that concepts of acceptability are complex and that the different dimensions of acceptability are inter-related. The thesis concludes with recommendations for future policy and service delivery of PrEP to at-risk groups in the UK.