Impulsivity explores the basis for the seemingly universal tendency to devalue rewards or punishments that are not immediately available. When confronted with any number of modern impulsive behaviors such as drug use, pathological gambling, marital infidelity, and gluttony individuals have a choice with two outcomes: an immediate benefit, such as getting high, or a delayed or probabilistic benefit, such as health, money saved, or the satisfaction of a good life. This volume is an approachable, comprehensive overview of the behavioral science and neuroscience of these impulsive choices and their relation to delay discounting--the tendency to devalue temporally distant rewards or punishments, even though they may greatly outbalance the immediate benefit of our choices. The cutting-edge researchers who contributed to this volume have documented cross-species similarities in impulsive decision making and pioneered the neuroscience of impulsive choice. In this text they provide insights into harmless impulsive acts as well as those that dominate and destroy lives. The contributors tackle key issues such as whether impulsivity and risk taking are a trait or state; the neuroscience, neuroeconomics, and computational modeling of neural systems underlying impulsivity; and the relation between impulsivity and addictions, health decision making, altruism, and attention-deficit disorder. Theoretical debates regarding the origins of impulsivity round out this text, which will be of interest to researchers and graduate students in psychology, behavioral economics, psychopharmacology, behavioral analysis and therapy, and the science of decision making.