For many years, data relating to the quality of water and sediment have been collected in the Galveston Bay system by a variety of organizations and individuals. The objectives of data collection have been equally varied, including the movement and properties of water, the biology of the bay, waste discharges and their impacts, navigation, geology, coastal processes, and fisheries. While the specific purposes of the individual data collection projects have limited each project in time and space, the data have great potential value to the Galveston Bay National Estuary Program (GBNEP) if they can be combined into a comprehensive data base yielding a historical depiction of the quality of the bay environment. The purpose of this project was to compile and evaluate these data, and to employ these data in a quantitative assessment of water and sediment quality of Galveston Bay and its evolution over time. There were three key objectives: (1) compilation of a comprehensive data base in machine-manipulable format; (2) analysis of space and time variation (i.e, 'trends') in quality parameters, i.e. characterization of the water and sediment quality of Galveston Bay; (3) identification of probable causal mechanisms to explicate the observed variations.