This book describes the Kluane Boreal Forest Ecosystem Project which operated from 1986 to 1996 in the southwestern Yukon. It begins by describing the area and its physical setting, and then the background of the project and the wisdom that had accumulated to 1986, on how this system might operate. The details of the experiments set up are presented, partly to help the reader appreciate the difficulty of working at -40 degrees and partly to aid the reader should they contemplate doing similar experiements in the future. Then they examine the three trophic levels of plants, the herbivores, and the predators in detail to provide some surprises about how the individual species operate within the overall system. Finally, they synthesize their findings in a model of the boreal forest vertebrate community, and provide an overview of what they have discovered and what remains to be done. Over the ten years of this project a large number of students and researchers have joined together to produce a picture which makes major advances in our understanding of the boreal forest ecosystem.