In the first section of this chapter, a simple general equilibrium model of an economy with nonmarket environmental and resource service flows is presented to show how the values of these flows emerge as shadow prices from the solution to a welfare maximization problem. The major types of methods for estimating values and benefits are then presented in the second section. The third section discusses some theoretical frameworks used in revealed preference models. The fourth section presents a simple model to illustrate the relationships between physical and biological changes in environmental and resource systems and the changes in well-being and values realized by the people affected by these changes. These models help to make clear the kinds of data required to carry out resource evaluations, and to show the roles of economists and physical and biological scientists in the evaluation process. The fifth section describes some issues about the noneconomic foundations of resource valuation. The chapter concludes with a discussion of the nature of cost in welfare theory.