While epidemiological and demographic data related to smoking are briefly reviewed, the major focus of this article is on the psychoactive effects of nicotine in reinforcing feelings of well-being and decreasing feelings of discomfort. Environmental and genetic factors can also influence smoking behavior. Self-administration, conditioned place preference, and drug discrimination studies have emphasized the reinforcing properties of nicotine. The development of tachphylaxis and chronic tolerance is also discussed. Human and animal studies have been used to examine the effect of nicotine withdrawal. 49 references