Understanding human decision-making is a key focus of behavioral economics, psychology, and neuroscience with far-reaching applications, from public policy to industry. Recently, advances in machine learning have resulted in better predictive models of human decisions and even enabled new theories of decision-making. On the other hand, machine learning systems are increasingly being used to make decisions that affect people, including hiring, resource allocation, and paroles. These lines of work are deeply interconnected: learning what people value is crucial both to predict their own decisions and to make good decisions for them. In this workshop, we will bring together experts from the wide array of disciplines concerned with human and machine decisions to exchange ideas around three main focus areas: (1) using theories of decision-making to improve machine learning models, (2) using machine learning to inform theories of decision-making, and (3) improving the interaction between people and decision-making AIs.