Environmental policy makers are faced with a difficult dilemma: On the one hand, technical expertise is a necessary but not sufficient condition to make prudent environmental decisions. Without input in form of public values and preferences, decisions cannot be legitimized. On the other hand, public perceptions are at least partially driven by biases, anecdotal evidence, false assumptions, about potential environmental impacts of human actions. We live in a pluralist society with different value systems and worldviews. Who can legitimately claim the right to select the values or preferences that should guide collective decision making, in particular when health and lives of humans are at stake? One of the answers to this question can be derived from the theory and practice of discursive deliberation. In the theory of communicative action developed by the German philosopher Juergen Habermas, the term discourse denotes a special form of a dialogue, in which all affected parties have equal rights and duties to present claims and test their validity in a context free of social or political domination. A discourse is called rational if it meets the following specific requirements: 1) seek a consensus on the procedure, 2) articulate and critique factual claims on the basis of the "state of the art" of scientific knowledge and other forms of problem-adequate knowledge, 3) interpret factual evidence in accordance with the laws of formal logic and analytical reasoning, 4) disclose their relevant values and preferences, thus avoiding hidden agendas and strategic game playing and process data and 5) arguments and evaluations in a structured format. A cooperative discourse is based on three steps:(1) Identification and selection of concerns and evaluative criteria. (2) The identification and measurement of impacts and consequences related to different policy options. (3) Conducting a discourse with randomly selected citizens as jurors and representation of interest groups as witnesses; The book describes the adaptation and implementation of the concept of the "cooperative discourse" illustrated by the example of the process of a site selection for a waste deposit plant.