This CD-ROM (Compact Disk - Read Only Memory) contains sidescan sonar, high-resolution seismic-reflection, bathymetric, textural, and bibliographic data and interpretations collected, compiled, and produced through the U.S. Geological Survey/State of Connecticut Cooperative and the Long Island Sound Environmental Studies Project of the Coastal and Marine Geology Program, U.S. Geological Survey during October 1991 to August 1998. Cooperative research with the State of Connecticut was initiated in 1982. During the initial phase of this cooperative program, geologic framework studies in Long Island Sound were completed. The second and current phase of the program, which is the focus of this CD-ROM, emphasizes studies of sediment distribution, processes that control sediment distribution, near-shore environmental concerns, and the relationship of benthic communities to sea-floor geology. The study area covers all of Long Island Sound, which is bordered on the north by the rocky shoreline of Connecticut, on the east by Block Island Sound, on the south by the eroding sandy bluffs of Long Island, and on the west by the East River and the New York metropolitan area. Sidescan sonar data were variously collected with 100 kHz Klein, Datasonics, and Edgetech systems under two survey schemes. In the first scheme, the data were collected along closely-spaced grids where the ship tracks were spaced 150 m apart and the sonar system was set to sweep 100 m to either side of the ship's track. This scheme produced the continuous-coverage acoustic images that are stored on the CD-ROM as TIF files. In the second scheme, the sidescan sonar data collected along reconnaissance lines spaced about 2,400 m apart. Only selected portions of this data, when used for geologic interpretation, are stored on this CD-ROM. Under both survey schemes, the sidescan sonar data were processed according to procedures summarized by Danforth and others (1991) and Paskevich (1992a, 1992b, 1992c). The seismic reflection data were variously collected with an Ocean Research Equipment 3.5-kHz profiler transmitting at a 0.25-s repetition rate and a Datasonics CHIRP system set to sweep between 2-7 kHz. Only selected seismic-reflection data, which are used as examples in geologic interpretations, are stored as GIF-formatted images on this CD-ROM. Navigation during this project was determined with a differential Global Positioning System (GPS); position data were logged at 10-second intervals. The bathymetric data were collected by means of a 200-kHz echo sounder and logged digitally. Surficial sediment (0-2 cm below the sediment-water interface) sampling completed as part of this project was conducted using a Van Veen grab sampler equipped with an Osprey video and still camera system. The photographic system was used to appraise bottom variability around stations, faunal communities, and sedimentary processes. It also documented bedrock outcrops and boulder fields where samples could not be collected. The fine fraction (less than 62 microns) was analyzed by Coulter Counter (Shideler, 1976); the coarse fraction was analyzed by sieving (gravel) and by rapid sediment analyzer (sand; Schlee, 1966). The data were corrected for the salt content of interstitial water. Size classifications are based on the method proposed by Wentworth (1929) and were calculated using the inclusive graphics statistical method (Folk, 1974), using the nomenclature proposed by Shepard (1954). A detailed discussion of the sedimentological methods employed are given in Poppe and others (1985); a detailed description of the methods used to perform the CHN analyses are given in Poppe and others (1996) . The database presented here contains over 14,000 records and 83 fields (see the Data Dictionary below). The specific fields and parameters have been chosen based on the data produced by the sedimentation laboratory of the Coastal and Marine Geology Program of the U.S. Geological Survey in Woods Hole, Mass., and the format of information typically found in the literature. Because the data have come from numerous sources, there are differing amounts and types of information. Most of the samples or sets of samples do not have data in all of the given fields. However, additional fields, qualifiers, and data can be added in virtually unlimited fashion to accommodate specific needs. The database itself is provided in four formats: Microsoft EXCEL, ver. 5, Quattro Pro for Windows, Dbase IV, and Tab-delimited ASCII text. Four bathymetric data sets are presented and include:1) Interpretations of the bathymetry within the continuous-coverage sidescan sonar study areas; 2} The NOS database modified to remove extraneous data (i.e. bouys); 3) Contoured National Ocean Service (NOS) bathymetry digitized by Applied Geographics Inc., Boston, Massachusetts; and 4) a fly-by based on the modified NOS database. Data files are present in ASCII format with navigation and depth in meters. The bathymetric interpretations within the sidescan sonar study areas are based on mean sea level and stored as TIF images; the NOS data are based on mean low sea level; and the fly-by is configured to run in QuickTime or MPEG, which can be downloaded from this CD-ROM. The bibliographic database, which contains over 2,000 references, is stored as an ASCII text, Microsoft Word, Corel WordPerfect, HTML, and Microsoft EXCEL files. This bibliography is largely a compilation of references from Lewis and Coffin (1985) and the GENCAT bibliographic database at the Long Island Sound Resource Center, Connecticut Department of Environmental Protection, Groton, Connecticut. These sources have been supplemented by citations from the BIOSIS, GEOREF, and FISH AND FISHERIES WORLDWIDE bibliographic databases.