Investment projects need to be evaluated by comparing their costs and benefits over their entire lifespan. The goal is to choose the project with the highest net present value (NPV), which means its benefits outweigh its costs. To do this, a discount rate called the economic opportunity cost of capital is used. If a project's economic NPV is positive, it's worth doing because it generates more benefits than using the resources elsewhere. If the NPV is negative, the project should be rejected because the resources could have been used more effectively elsewhere. This chapter explains how to calculate the economic present value of an investment using the economic opportunity cost of capital.