Two types of behavioral measure are primarily used to examine impulsivity in humans and animals: Go/No-go tasks to assess inhibition and relative preference tasks to assess delay aversion. Several examples of each type of task are described so that common cognitive processes and variables affecting performance can be identified. Data suggest that smokers are more impulsive on each of these impulsivity measures than nonsmokers. Several models can be proposed to account for this group difference: (a) the differences predate and, possibly, are causally related to the initiation of cigarette smoking; (b) higher levels of impulsivity are associated with continued smoking, either through an association with heightened positive subjective effects of nicotine or heightened negative effects of nicotine abstinence (withdrawal); (c) nicotine causes neuroadaptations that result in elevated impulsivity in smokers. Studies relating to each of these models are reviewed, and it is concluded that all three models may contribute to the observed higher levels of impulsivity in smokers. However, pertinent studies are limited and additional systematic research is needed.