The smoking cessation clinical practice guideline recently published by the Agency for Health Care Policy and Research (AHCPR) summarizes current knowledge on smoking cessation treatments. Among its recommendations, the guideline encourages physicians to motivate patients who indicate that they are not yet ready to quit smoking. Because medical training typically emphasizes pharmacologic rather than behavioral treatment, we believe that physicians caring for cancer patients may benefit from more extensive instruction in motivating patients to quit smoking. This article describes how a contemporary theoretical approach, the transtheoretical model of change, can be used to promote behavioral change. Multiple studies, primarily in the field of smoking cessation, provide strong empiric support for use of this model in clinical practice. The model consists of five stages of smoking cessation that describe different levels of readiness to quit: precontemplation, contemplation, preparation, action, and maintenance. A diagnostic tool is presented, and specific smoking cessation counseling strategies are suggested for each stage of change. Implications for the use of the model by physicians who counsel and treat smokers are discussed.