Low patient cooperation erodes many of the proven benefits of antihypertensive therapy. Over the last few years, there have been important advances in our understanding of the nature and management of patient compliance in hypertension and other chronic illnesses. In this article we review the theoretical foundation of compliance behavior; methods of measuring compliance; established and promising approaches to managing compliance; ethical considerations in measuring, improving, and researching compliance; the current state of implementation of compliance techniques in practice settings; and the efforts to disseminate information on compliance through undergraduate and continuing health professional education programs. (Hypertension 4: 415–423, 1982)