Southern Africa has the worst HIV/AIDS epidemic in the world. In some states the HIV prevalence is close to 40% of the adult population. This thesis shows that, in spite of the formal commitment of Southern African governments to follow the international guidelines for fighting the epidemic and the financial and technical support of powerful donors, three regional states - Botswana, Mozambique and South Africa - presented significant variations in the domestic assimilation of internationally-devised prescriptions for HIV/AIDS action. These international policy guidelines are based on an innovative conceptualisation of security that proclaims the global epidemic a threat to international peace and stability. Drawing upon a new theoretical synthesis between the constructivist literature on international norms and the securitisation scholarship, the study provides an analytical framework for understanding the global securitisation of HIV/AIDS as an international norm. The HIV/AIDS securitisation norm (HASN) is an attempt by the present work to combine in a single concept the myriad of ideas and international prescriptions about HIV/AIDS interventions. By analysing the incorporation of HASN in these three Southern African states, which are highly impacted by HIV/AIDS, the study demonstrates that pre-existing political cultures and social practices have defined quite different policy outcomes and domestic interpretations of transnational (security) understandings of the epidemic.