Decision making, the process of choosing between options, is a fundamental human behavior that has been studied intensively by disciplines ranging from cognitive psychology to economics. Despite the importance of this behavior, the neural substrates of decision making are only beginning to be understood. Impaired decision making is recognized in neuropsychiatric conditions such as dementia and drug addiction, and the inconsistencies and biases of healthy decision makers have been intensively studied. However, the tools of cognitive neuroscience have only recently been applied to understanding the brain basis of this complex behavior. This article reviews the literature on the cognitive neuroscience of human decision making, focusing on the roles of the frontal lobes, and provides a conceptual framework for organizing this disparate body of work.