POE is now 25 years old. Phases in the development of POE in the 1960's, 70's and 80's are examined and characteristics of POEs in these decades are discussed in terms of the 1) types and size of buildings evaluated 2) variables included in the evaluation 3) the relationships among the variables and 4) intentions of the investigation. POE has evolved from research into a applications-oriented activity over the past three decades. Building types and clients have also changed - in the U.S. large, private sector firms are increasingly utilizing POE. Research in POE also continues emphasizing the interaction between, and the relative influence of environmental and non-environmental variables, as well as the development of databases for POE utilization.