Introduction: The U.S. Geological Survey (USGS) Fourth Biennial Geographic Information Science (GIS) Workshop (USGS-GIS 2001) was held April 23-27, 2001, at the Denver Federal Center in Denver, Colorado. The workshop provided an environment for participants to improve their knowledge about GIS and GIS-related applications that are used within the USGS. Two major topics of USGS-GIS 2001 were the application of GIS technology to interdisciplinary science and the distribution and sharing of USGS GIS products. Additionally, several presentations included GIS technology and tools, project applications of GIS, and GIS data management. USGS-GIS 2001 included user and vendor presentations, demonstrations, and hands-on technical workshops. Presentation abstracts that were submitted for publication are included in these proceedings. The keynote speaker was Karen Siderelis, the USGS Associate Director for Information (Geographic Information Officer). In addition to the USGS, other Federal agencies, GIS-related companies, and university researchers presented lectures or demonstrations or conducted hands-on sessions. USGS employees and contractors from every discipline and region attended the workshop. To facilitate the interaction between the Federal agencies, each of the presenting Federal agencies was invited to send a representative to the workshop. One of the most beneficial activities of USGS-GIS 2001, as identified by an informal poll of attendees, was the Monday evening poster session in which more than 75 poster presentations gave attendees a chance to learn of work being performed throughout the USGS. A feature new to USGS-GIS 2001 was internet participation of USGS personnel through cyber seminars of the morning plenary sessions.