Ecological interactions can be divided into 3 main direct types: competition where organisms induce costs on each other, predation where some benefit and others suffer costs from the interaction, and mutualism where all organisms benefit. Mutualism is the most enigmatic and least studied of the tree and yet may be the most important. The mutualism between mycorrhizal fungi and plants may be especially important and responsible for plant colonization of land. In this mutualism, plants trade carbon, which they are more efficient at obtaining, with the fungi for nitrogen, phosphorous, and other minerals, which they are more efficient at obtaining. I hope to use game theory and greenhouse experiments to see how mutualisms originate and determine the ecological and environmental conditions which maintain them. This work is currently funded by the National Science Foundation as part of a Postdoctoral Ressearch Fellowship in Biology.