The goal of this paper is to provide a conceptual model to underpin plans for restoration of salmon, resident fishes and other key attributes of the Klamath River Ecosystem. We include boundaries, principles, and assumptions for the Klamath River Ecosystem, with a scientific retrospective analysis serving as the basis for our conceptual model. The authors represent a broad range of professional expertise with many years of
research and management experience in the Klamath and other western USA rivers.We start with our view of what a conceptual model should be and then move to descriptions of Klamath Basin physiography and geopolitics. Then we present a retrospective analysis of Klamath biogeography and human influences on aquatic species in relation to functional domains of the river system. The paper concludes with our conceptual model for the Klamath River Ecosystem as derived from our collective understanding of natural and cultural attributes, interactions, constraints and opportunities.