Narragansett Bay is a bay and estuary on the north side of Rhode Island Sound. Covering 147 mi² (380 km²), the Bay forms New England's largest estuary, which functions as an expansive natural harbor, and includes a small archipelago.

While there are over thirty islands in the bay the three largest are Aquidneck Island, Conanicut Island, and Prudence Island. Bodies of water that are part of Narragansett Bay include the Sakonnet River; Mount Hope Bay; and the southern, tidal part of the Taunton River. The bay opens on Rhode Island Sound and the Atlantic Ocean; Block Island lies less than 20 miles from its opening. Bridges over parts of the bay include two suspension bridges, the Claiborne Pell Newport Bridge and Mount Hope Bridge, the Jamestown-Verrazano Bridge, and the Braga Bridge which forms the Narragansett Bay crossing of United States Interstate 195.