Understanding individual differences in smoking behavior and nicotine dependence can increase knowledge of smoking dynamics and aid in the development of treatment regimens. Nicotine dependence among smokers is variable, and in some cases, fails to develop even after years of smoking. This variation can influence treatment outcome and presents a challenge to treatment developers. Gender differences are evident sometimes in smoking prevalence, in smoking cessation, and smoking rate. Gender, however, may be a superficial indicator; reasons for smoking, individual reactions to nicotine, and cultural sanctions and role definitions may be more influential. Analyses of individual differences should focus on identifying the underlying processes that control smoking behavior.