A modeling framework was constructed for the Chesapeake Bay system to provide a credible basis to assist the decision-making process and to further the understanding of Bay water quality processes and the sensitivity of such processes to external nutrient loading. The modeling structure consists of a Watershed Model to generate nutrient loads from the Bay sub-basins; a three-dimensional, time variable hydrodynamic model; and a three-dimensional, time variable model of water quality coupled to a model of sediment chemistry. Extensive calibration analyses of the entire modeling structure was conducted using data collected primarily during a three year period from 1984-1986. The Chesapeake Bay Program Modeling Subcommittee completed its initial review of the Chesapeake Bay Water Quality Model (CBWQM) calibration in May 1991 and concluded the model could provide useful information to the Bay community, especially with respect to dissolved oxygen problems in the deep water of the main Bay. Final calibration of the CBWQM was completed in January 1992.