This article examines the dynamic role of law as a tool, and potential barrier, to public health interventions designed to ameliorate the negative impacts of human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) globally. Law impacts the lives of persons living with (and at risk of) HIV/AIDS in many ways. Laws may: (1) help to ensure that public health authorities are empowered to provide effective prevention and treatment programmes; (2) effectuate the human rights to life, health, work, education and property ownership of persons living with, or at risk of, HIV/AIDS; and (3) protect persons living with HIV/AIDS from social risks, stigma and other harms by respecting privacy and prohibiting unwarranted discrimination. However, laws can also create legal barriers in many countries that impede effective HIV/AIDS interventions by penalizing those with HIV/AIDS through criminal sanctions or other policies. As a result, it is recommended globally that laws should facilitate the prevention and treatment of HIV/AIDS consistent with scientific and public health practices and with a human rights framework. Effective use of existing laws that promote the public's health, and reforms of laws which impede it, contribute to improved individual and communal health outcomes concerning HIV/AIDS.