Human ingenuity offers the best hope for tackling a whole range of environmental problems currently threatening global welfare, yet the human mind also creates cognitive barriers to wise environmental agreements. In this article, the authors focus on a set of six systematic cognitive barriers that are particularly endemic to environmental disputes. The fixed-pie bias grows from the assumption that disputants' interests are perfectly opposed. This mythical fixed pie inhibits the discovery of beneficial trade-offs that integrate parties' interests. The authors also discuss five other cognitive biases that combine with the fixed-pie assumption to influence the resolution of disputes in the environmental domain: pseudosacredness, egocentrism, overconfidence, unrealistic optimism, and endowment effects. They discuss the potential role of learning and experience in improving negotiator performance and conclude with prescriptive advice for overcoming these cognitive barriers.