This dissertation developed an eclectic theory of environmental mediation and submitted it to 31 environmental mediation experts for an assessment of the 63 propositions of the theory. The propositions which represented factors which the mediation experts assessed as important elements contributing to effective mediation were grouped into an ''Essential Model," and the propositions which represented less important elements contributing to effective mediation were grouped into a "Secondary Model." Key dimensions which distinguish the two models were identified. The eclectic theory was developed from the case and theoretical literature, and practitioner comments on the art of environmental mediation. The expert assessment was conducted by submitting an instrument containing 63 propositions to the 31 mediation experts with a request that they rate the importance of each proposition in contributing to effective environmental mediation outcomes. The dissertation presents three alternative general models of mediation, and compares and contrasts the practice of environmental mediation with these models. Recommendations for further research are made, and critical reflections on the state of the art of environmental mediation are presented. / Ph. D.