The theory of the measurement of welfare change has been discussed by others, both at the most rigorous levels of abstraction, and in pragmatic, practical terms of application. See for examples, Johansson (1987), Just, Hueth, and Schmitz (1982, 2004), and Bockstael and McConnell (2007). The earliest work focused on the welfare effects of changes in the prices people pay for the (private) goods they consume, but the literature has expanded broadly into valuing changes in the quantity and quality of both private and public goods. The current chapter provides a systematic development of the definition and measurement of the welfare effects stemming from changes in prices and the quantities and/or qualities of nonmarket environmental and resource service flows.