This multi-site collaborative study integrates medication adherence data with patient demographic, psychosocial characteristics and behavioral, virologic and clinical outcomes data collected from 2,830 individuals across 15 studies from 13 major institutions. The goals are to: 1) create a powerful data source to address questions that cannot be answered with any single data set; 2) create and validate adherence measures that can characterize multi-faceted adherence behavior fully, objectively and accurately; 3) study the patterns and determinants of adherence to antiretroviral medications and evaluate the effectiveness of interventions with the large, diverse HIV+ populations; and 4) model virologic outcomes, clinical events, disease progression and death as functions of adherence to antiretroviral medications, and patient, medication and regimen characteristics over time.