Legislative trends in the United States, the United Kingdom, and many other countries require accurate and efficient assessment of environmental aesthetics. Most of this assessment is currently undertaken using traditional design judgment, but when the powers of the government are used to enforce policy the scope of the aesthetic evaluation requires consideration of questions such as: what concepts will aesthetic decision makers need to perform their intended function?; how can they obtain the information they need?; and what is currently known about environmental aesthetics?. This text aims to answer these questions with a logical theory of environmental aesthetics, empirical evidence covering 277 studies, 41000 respondents and 12000 stimuli, and seven case histories showing how the theory can be applied to actual aesthetic decisions. It proposes a unified protocol for measuring the magnitude of aesthetic impacts. It also applies that protocol to 94 specific findings which span a wide range of issues.