Scientific goals: (1) To determine how activity space, as assessed with geographical momentary assessment (GMA), influences HIV status, knowledge of HIV-related healthcare and likelihood of seeking care, and risk/transmission behavior. (2) To determine differences in activity spaces between HIV-positive people and HIV-negative people in their social networks. (3) To assess the effects of mental health and cognition (executive function, impulsivity) on differences in activity spaces between HIV-positive and HIV-negative people. (4) To explore the role of phylogenetics and its interplay with environment in regards to drug use initiation, HIV risk as it relates to drug use, drug injection, and needle sharing. (5) to assess EMA reports of drug use and psychosocial stress as well as real-time environmental risk exposure among individuals with and without HIV.