Publisher Summary This chapter focuses on incentive theory and changes in reward. Changes in incentive motivation are essential aspects of contemporary theories of learning, but little attention has been paid to the rate at which such changes take place. If the incentive motivation is mediated by a response mechanism, then the laws of classical conditioning would suffice to describe incentive change effects. Incentive motivation is only one of the conceptual determinants of instrumental performance, and hence cannot be measured directly. Nevertheless, it is assumed that choice between two alternatives that are otherwise equivalent can be used to index their relative incentive values. The rate at which incentive motivation changes in response to a change in the reward conditions was evaluated empirically in the chapter by using a choice procedure with rats as subjects. The assumption of invariant rates of change in incentive motivation is a tenable one. When the incentive value of the reward received after a response differs from the preexisting incentive motivation for that response, an appropriate change occurs at a rate that is more or less independent of prior experimental history.