A new shoreline file has been created for Boston Harbor by digitizing and combining the most recent charts. Up-to-date digital shoreline files are required to support coastal geographic information system (GIS) displays that combine data from multiple sources. A second objective was to compare the Boston Harbor data set with earlier shoreline data sets, such as the Massachusetts Coastline (1:25,000) derived from USGS DLG topographic data (MCOAST), and NOAA’s Medium Resolution Digital Vector Shoreline (1:70,000), and recent, high-resolution orthophotographic coverage. Comparisons reveal changes due to coastal construction as well as discrepancies that need resolution. The present data set represents the most detailed delineation currently available.