Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 14.I wrote this book in response to a need expressed by one of my Ph.D. students, David Merritt, who walked into my office one afternoon for a summary reference on mountain rivers. Search as I might, I could not find such a reference in my files. I did find a stack of individual articles, however, and sent David on his way loaded up with them. As I thought about it, I realized that a summary reference on mountain rivers could be very useful, particularly given the increasing interest in the subject that I have noticed these last few years. Thus I began to write a review of the fluvial geomorphology of mountain rivers and, as such volumes will, this grew into a broader review of physical, biological, and chemical characteristics of mountain rivers, and of human interactions with these rivers.