This volume contains a collection of short papers that document some of the conclusions and results of on-going investigations related to ground-water resources of the Middle Rio Grande Basin, New Mexico. These results, and additional project reports, were presented at the Fourth Annual Middle Rio Grande Basin workshop convened in Albuquerque during February 2000. The workshop was jointly sponsored by the U.S. Geological Survey and the New Mexico Bureau of Mines and Mineral Resources as a forum for public presentation and discussion of multidisciplinary studies conducted during the previous 4 years. This considerable body of work was undertaken to improve the scientific understanding of factors that control ground-water availability and quality, and to explore land-surface characteristics that have affected the development and use of this valley that currently supports a population in excess of 600,000.