Self-efficacy, a core construct of Bandura's social cognitive theory, has wide appeal and usefulness in the health and social sciences. Self-efficacy is frequently used across disciplines to assess an individual's beliefs about her likelihood to engage in a certain behavior. Because of the behavioral-change approaches common in rehabilitation counseling interventions, self-efficacy is an important construct to operationalize, measure, and apply for best research and clinical outcomes. Several factors contribute to inaccurate or inappropriate assessment, measurement, interpretation, and application of this important construct; numerous scales used to measure efficacy, various contexts, related constructs, and moderating effects of efficacy make best use of efficacy measurement and application difficult. This article outlines the theory of self-efficacy, distinguishes its closely related constructs, summarizes common moderating effects, and provides important considerations for clinical practice and research. (Contains 2 tables.)