Cost-effectiveness analysis is a common tool for ascertaining the efficiency of investment, but it has only rarely been applied to education. This chapter begins by defining cost-effectiveness and addressing the rationale for using cost-effectiveness in education. It proceeds to issues in measuring educational effectiveness using a common metric across interventions. It then devotes considerable attention to how to apply the concept of opportunity cost to cost measurement in education using the ingredients method, which relies on specifying the required resources and their market or shadow prices. It concludes with a sampling of cost-effectiveness studies devoted to different educational topics: teacher selection, dropout prevention, early reading achievement and multiple reforms. The article concludes with future directions.