The modeling of crustal deformation crosses several scientific disciplines including geodesy, tectonophysics, seismology, volcanology, hydrology, and geology. The AGU Conference on Time-Dependent Positioning provided scientists from these disciplines an opportunity to exchange information on alternative modeling concepts and techniques. The conference's scope encompassed user requirements for crustal motion models, the theoretical nature of crustal motion, modeling methodology, and results from recent deformation studies. The conference was convened September 23–25, 1991, in Annapolis, Md. It featured 62 presentations and was attended by 90 scientists from seven countries. Partial funding was provided by the National Aeronautics and Space Administration, the National Oceanic and Atmospheric Administration, the National Science Foundation, and the U.S. Geological Survey.