This report describes the water resources of Massachusetts. It contains sections describing the location, use, quality, and management of water resources in Massachusetts, followed by a summary of the surface water and ground-water resources of all 27 river basins designated by the State for planning purposes. The data for each basin include information about selected continuous record streamflow-gaging stations, the distribution and size of major lakes and streams, and the character of the principal aquifers. Each basin summary is accompanied by a map that shows basin and political boundaries, hydrography, locations of continuous-record streamflow-gaging stations, and aquifer areas. The aquifer areas were derived from the Hydrologic Investigations Atlases and generally show areas that are likely to yield 100 gallons per minute or more to individual wells. The report was compiled from many reports, including 30 U.S. Geological Survey Hydrologic Investigations Atlases that inventory water resources of the State.