Four factors which influence smoking treatment outcome are identified: environmental variables, client characteristics, process variables, and specific treatment approaches. Important environmental factors are stress and social support. Of client characteristics, sex is the best predictor of treatment success. Men are more likely to quit and maintain abstinence than women. However, the majority of women alter their smoking habits during pregnancy. Low-income persons and ethnic minorities are underrepresented among subjects in treatment studies and have larger percentages of smokers in the population at large. Extraverted smokers are more likely to begin to smoke and have difficulty quitting. Also, the more anxious, poorly adjusted smoker has more trouble quitting than the less troubled smoker. The higher the client's sense of self-efficacy, the better the chance of that person entering treatment and doing well. Furthermore, smokers who take in lower levels of nicotine are more successful at quitting. Many process questions are suggested. Few have been approached empirically. The effectiveness of ex-smokers as therapists in smoking cessation programs has not been systematically investigated, even though the smoking history of therapists is a question frequently asked by clients. We suggest that the skill and empathy of group leaders is more important than smoking history. Smoking therapists should be aware of nonspecific treatment factors such as positive expectations, social reinforcement, and self-disclosure which may have a powerful influence on the efficacy of smoking treatment. Specific treatment approaches were classified into three categories: low-contact approaches, including educational, self-help, and minimal treatment approaches; psychological treatments; and pharmacological treatment. Education, self-help, and minimal treatment approaches are thought to be accretively effective when the large size of the audience is considered. Also, innovative treatments which address the influence of social support systems and physiological addition are promising treatments for individuals requiring a structured or intensive method of quitting.