Traditionally, instrumental or operant reinforcement has been considered to be the process by which the majority of an organism’s “meaningful” behavior is generated (cf. Skinner, 1938; Blackman, 1974). The importance of instrumental learning to the animal psychologist arises from a couple of factors. First, instrumental learning as championed by B. F. Skinner provided a suitable atheoretical means of describing learning phenomena in terms of behavior-environment interactions. Second, from an adaptive point of view, if an animal failed to learn about the consequences of its actions then it would surely be at an extreme disadvantage — most organisms are in some way sensitive to the consequences of their actions, although this of course does not necessarily mean that they learn about the consequences of those actions. Learning to adapt to the consequences of its actions is therefore a useful psychological tool for an animal that lives in a changing and unpredictable environment.