Book excerpt: contributors - biologists, ecologists, geomorphologists, historians, hydrologists, lawyers, and political scientists - weave together threads from their diverse perspectives to reveal the processes that shape the past, present, and future of the San Pedro's riparian and aquatic ecosystems. They review the biological communities of the San Pedro and the stream hydrology and geomorphology that affects its riparian biota. They then look at conservation and management challenges along three sections of the San Pedro, from its headwaters in Mexico in its confluence with the Gila River, describing legal and policy issues and their interface with science; activities related to mitigation, conservation, and restoration; and a prognosis of the potential for sustaining the basin's riparian system." "Complemented by a foreword written by James Shuttleworth, these chapters demonstrate the complexity of the San Pedro's ecological and hydrological conditions, showing that there are no easy --