The theory of costs is a cornerstone of the economic way of thinking. From Principles classes to the most advanced academic literature, costs play a vital role in explaining virtually all human behavior and economic outcomes. This volume explores and develops a rich literature on costs by examining the many roles that costs play in economic theory and practice. The essays study both influential traditions in economics and neglected insights and the result is a wide-ranging interdisciplinary study of costs. It will serve as a valuable source of discussion and debate, and act as a platform for further research on these central economic issues.