Comorbidities are additional chronic conditions that may compromise the health of people living with HIV. Some “comorbid” conditions are more common in people with HIV because they have similar risk factors or because the immune changes associated with HIV infection or the side effects of antiretroviral drugs increase a person’s risk of developing them. These comorbidities are now the most common causes of death and disability in people living with HIV. Research on comorbidities aims to understand the underlying links between comorbidities and HIV, and to develop treatment strategies and guidelines to reduce their impact on the lives and well-being of people living with HIV.