HIV transmission remains a significant public health concern, especially among men who have sex with men (MSM). Condomless anal intercourse (CAI) continues to be the major route of transmission for MSM. Thus, to reduce the incidence of HIV, it is critical to identify how contextual risk factors influence CAI and develop behavioral strategies that modify risk factors directly or reduce their influence on behavior. This study will examine the mechanisms through which one of the central contextual risk factors, heavy drinking, influences sexual decision processes in the natural environment and test the benefit of a brief intervention designed to reduce sexual risk behavior among those who engage in heavy drinking.