Motivation is often regarded as a client attribute related to maladaptive defense mechanisms, and it is used to explain unfavorable treatment outcome. This article provides an integrative review of research relating motivational variables and interventions to treatment entry, compliance, and outcome; special focus is on alcoholism and other addictive behaviors. Empirical evidence is considered regarding motivational interventions including advice, feedback, goal setting, role playing, modeling, contingencies, continuity of care, voluntary choice, and modification of behavior attractiveness. Beyond these specific interventions, nonspecific aspects of motivation are reviewed including client characteristics (distress, self-esteem, locus of control, severity, conceptual level), environmental variables, and therapist characteristics (hostility, expectancy, empathy). A dynamic conceptualization of treatment motivation is proposed as an alternative to a trait model.