An issue facing the citizens and governments of modern democracies is the direct participation of the public in the solution of environmental problems. Governments are increasingly experimenting with approaches that give citizens a greater say in the environmental debate. A crucial question is addressed: how can we measure the performance of the citizen participation process? An approach to the problem is taken by viewing public participation as an act of communication. Drawing on Jurgen Habermas' "Critical Theory of Communication", a normative framework is developed around the central area of citizen participation and competence in knowledge verification. A theoretical and methodological basis for the systematic evaluation of models for environmental discourse is provided. Eight models of citizen participation are studied, from North America and Europe. Each model is evaluated and criticized in paired chapters written by scholars.