Abstract: To a first approximation, decision making is a process of optimization in which the decision maker tries to maximize the desirability of the outcomes resulting from chosen actions. Estimates of desirability are referred to as utilities or value functions, and they must be continually revised through experience according to the discrepancies between the predicted and obtained rewards. Reinforcement learning theory prescribes various algorithms for updating value functions and can parsimoniously account for the results of numerous behavioral, neurophysiological, and imaging studies in humans and other primates. In this article, we first discuss relative merits of various decision-making tasks used in neurophysiological studies of decision making in nonhuman primates. We then focus on how reinforcement learning theory can shed new light on the function of the primate dorsolateral prefrontal cortex. Similar to the findings from other brain areas, such as cingulate cortex and basal ganglia, activity in the dorsolateral prefrontal cortex often signals the value of expected reward and actual outcome. Thus, the dorsolateral prefrontal cortex is likely to be a part of the broader network involved in adaptive decision making. In addition, reward-related activity in the dorsolateral prefrontal cortex is influenced by the animal's choices and other contextual information, and therefore may provide a neural substrate by which the animals can flexibly modify their decision-making strategies according to the demands of specific tasks.