Presently in Yellowstone there are almost 200 active research permits that involve over 500 investigators, but only a small fraction of this scientific work is reported in the popular press. Furthermore, the results are mixed and frequently confusing to the general public. The intent of this book is to explain both the general issues associated with the region and how science is done to understand those issues, from wolf and grizzly bear research to thermal activity. It further describes how science informs policy in the Greater Yellowstone Region, how scientists from an array of disciplines do their work, and finally, how the nature of that work enables or limits future plans for managing the park and surrounding lands.