The drive to seek rewards – for example, food, water, or social interactions – shape most of our behaviors. How do animals learn which actions will lead to reward? How do rewards shape decisions? How is the underlying circuitry altered in disease states? Decades of experimental and theoretical work have led to several influential hypotheses about how the striatum – a major hub in the reward circuit – mediates these functions. However, due to technical limitations, it has been difficult to test these ideas rigorously. By integrating a wide range of technical approaches – optogenetics, rodent behavior, electrophysiology, imaging, and computational modeling – our lab is providing new insights into the circuit level mechanisms underlying these fundamental processes.