This thesis examines the underlying cause of social stigma towards people living with HIV, and the extent to which it discourages HIV testing and treatment. We use a discrete choice model to describe a person’s decision to seek treatment for HIV (antiretroviral therapy or ART), and estimate the social cost of seeking treatment using administrative health records from southern Malawi. We show that seeking ART at a clinic where many other community members are present carries a significant cost, even after taking into account clinic quality and location. We investigate the theoretical effects of policy interventions designed to reduce stigma and other barriers to care, and demonstrate important complementarities between such policies. We next evaluate a cluster-randomized information experiment in Zomba, Malawi designed to correct a common misconception: most do not know that ART drugs have a public benefit, that is, the medication prevents HIV transmission between sexual partners. We microfound HIV stigma as sexual discrimination between sexual partners, and model the decision to seek an HIV test (and then, if required, medical treatment) as a signal of infection. We show, theoretically and empirically, that the randomized information intervention reduces this type of stigma and significantly increases the rate of HIV testing. The results demonstrate that social stigma is an important barrier to HIV testing and treatment, that stigma can be due to rational behavior by a misinformed public, and that providing new information can be an effective way to mitigate its effects.