Delaware Bay is the estuary outlet of the Delaware River on the northeast seaboard of the United States. Approximately 782 square miles (2,030 km2) in area, the bay's fresh water mixes for many miles with the salt water of the Atlantic Ocean.

The bay is bordered inland by the States of Delaware and New Jersey, and the Delaware Capes, Cape Henlopen and Cape May, on the Atlantic. The Delaware Bay is bordered by six counties: Sussex, Kent, and New Castle in Delaware, along with Cape May, Cumberland, and Salem in New Jersey. The Cape MayLewes Ferry crosses the Delaware Bay from Cape May, New Jersey, to Lewes, Delaware. Management of ports along the bay is the responsibility of the Delaware River and Bay Authority.

The shores of the bay are largely composed of salt marshes and mudflats, with only small communities inhabiting the shore of the lower bay. Besides the Delaware, it is fed by numerous smaller rivers and streams, including (from north to south) the Christina River, Appoquinimink River, Leipsic River, Smyrna River, St. Jones River, Mispillion River, Broadkill River and Murderkill Rivers on the Delaware side, and the Salem River, Cohansey River, and Maurice Rivers on the New Jersey side. Several of the rivers hold protected status for their salt marsh wetlands bordering the bay, which serves as a breeding ground for many aquatic species, including horseshoe crabs. The bay is also a prime oystering ground.

The Delaware Bay was designated a Ramsar Wetland of International Importance on May 20, 1992. It was the first site classified in the Western Hemisphere Shorebird Reserve Network.

Henry Hudson (c. 1565 – disappeared 23 June 1611) was an English sea explorer and navigator during the early 17th century, best known for his explorations of present-day Canada and parts of the northeastern United States.

In 1607 and 1608, Hudson made two attempts on behalf of English merchants to find a rumoured Northeast Passage to Cathay via a route above the Arctic Circle. In 1609, he landed in North America on behalf of the Dutch East India Company and explored the region around the modern New York metropolitan area. Looking for a Northwest Passage to Asia on his ship Halve Maen ("Half Moon"), he sailed up the Hudson River, which was later named after him, and thereby laid the foundation for Dutch colonization of the region.

On his final expedition, while still searching for the Northwest Passage, Hudson became the first European to see Hudson Strait and the immense Hudson Bay. In 1611, after wintering on the shore of James Bay, Hudson wanted to press on to the west, but most of his crew mutinied. The mutineers cast Hudson, his son, and seven others adrift; the Hudsons and their companions were never seen again.