The second study that is currently open for enrollment at the PIC Partners Study. The PIC Partners Study is an observational study enrolling sex and needle-sharing partners of people who enroll in the main PIC natural history study. The goal of this study is to try to understand the characteristics of partners and their HIV virus that may influence HIV transmission. Examples of some of these partner characteristics include type of sexual contact, clinical stage of disease and viral load, antiretroviral treatment, circumcision, other sexually transmitted infections (particularly genital ulcer diseases like herpes or syphilis), and genetics (like HLA typing) of transmitting partners. Participants in this study will have from one or three visits over approximately one month. The study provides HIV tests to screen for HIV infection and CD4 and viral load testing for HIV-positive partners.