Most studies examining HIV antiretroviral medication treatment adherence involve quantitative surveys. Although these studies have identified factors associated with medical adherence, no single variable or combination of variables is sufficiently consistent to apply to any individual or group of people. Using qualitative methods, an ethnically diverse sample (N=110) of HIV+ women, men who have sex with men, and male injecting drug users in four U.S. cities were interviewed in depth to elicit their experiences, perspectives, and life contexts regarding knowledge, attitudes, beliefs, and experiences with HIV medication adherence. Most described multiple influences on medication-taking behavior, describing adherence as a dynamic phenomenon that changes over time with their changing beliefs, attitudes, emotions, and daily and larger life events. Prevalent themes include ambivalence toward HIV medication and intentional nonadherence, usually to address physical side effects. Factors from different domains (e.g., cognitive, emotional, interpersonal) can have compensatory influences on behavioral outcomes. Findings are discussed in terms of social action theory, contributing to our theoretical understanding of the phenomenon of adherence.