This issue of Clinics in Perinatology, guest edited by Drs. Athena Kourtis and Marc Bulterys, examines Perinatal HIV/AIDS. Authorities in the field have come together to offer reviews on topics including Epidemiology of perinatal HIV infection: US and worldwide; Biology of perinatal HIV transmission: Timing, virologic and immunologic factors; Viral sequencing from HIV-infected mothers and infants: Molecular evolution, diversity, and risk factors for mother-to-child transmission; Diagnosis of perinatally-acquired HIV infection; Prevention of mother-to-child transmission of HIV: Antiretroviral strategies; Prevention of mother-to-child transmission of HIV: The role of Cesarean section; International recommendations for prevention of mother-to-child transmission of HIV; Immune-based approaches: active and passive immunization; Breastfeeding and HIV: Biology of transmission and current state-of-the-art regarding prevention; HIV drug resistance and mother-to-child transmission of HIV; Survival and health benefits of breastfeeding versus artificial feeding in infants of HIV-infected women: Developing vs. developed world; Clinical care of the HIV-exposed infant of HIV-infected mothers; Clinical care of the HIV-infected infants; Issues of prematurity and HIV exposure/infection; and Antiretroviral pharmacology: Special issues regarding pregnant women and neonates.