This first part of a 2-part issue of Infectious Disease Clinics, edited by Michael S. Saag, MD and Henry Masur, MD, is devoted to HIV/AIDS. This issue will cover global epidemiology; testing, staging, and evaluation; linkage to care, retention in care; antiretroviral therapy: current drugs, when to start, what to start, failure; update on opportunistic infections; HIV co-morbidities; and co-infection Hepatitis B and Hepatitis C.