The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.

It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S. states of New Hampshire and Maine, as well as Massachusetts north of Cape Cod, and the southern and western coastlines of the Canadian provinces of New Brunswick and Nova Scotia respectively.

Both Massachusetts Bay and the Bay of Fundy are included within the Gulf of Maine system. As such, the Gulf of Maine is also home to the highest tidal variations on the planet (see Bay of Fundy for further information).

The coastline of the Gulf of Maine is predominantly rocky and scenic; the only significant coastal developments are located in the Boston, Portsmouth, Portland and Saint John metropolitan areas. The effects of glaciation are responsible for stripping sedimentary soil away from the coastline, therefore the gulf lacks the sandy beaches found to the south along the Eastern Seaboard. The underwater features of the seabed sculptured during the lower sea levels of the ice ages make the gulf a semi-enclosed sea bounded to the south and east by underwater banks. Georges Bank in particular, on its southern end, protects the Gulf of Maine waters from the Gulf Stream. Gulf of Maine waters are more strongly influenced by the Labrador Current, making the gulf waters significantly colder and more nutrient-rich than those found to the south. Undersea valleys in the central basin can reach depths of 1,500 feet (500 m) while undersea mountains rise up 800 feet (266 m) from the sea floor, almost reaching the surface in some locations, or even exceeding it, creating islands.

Maine (ⁱ/ˈmeɪn/) is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost portion of New England. It is known for its scenery—its jagged, mostly rocky coastline, its low, rolling mountains, its heavily forested interior and picturesque waterways—as well as for its seafood cuisine, especially lobsters and clams.

For thousands of years, indigenous peoples were the only inhabitants of the territory that is now Maine. At the time of European encounter, several Algonquian-speaking peoples inhabited the area. The first European settlement in Maine was by the French in 1604 on Saint Croix Island, by Pierre Dugua, Sieur de Mons. The first English settlement in Maine, the short-lived Popham Colony, was established by the Plymouth Company in 1607. A number of English settlements were established along the coast of Maine in the 1620s, although the rugged climate, deprivations, and conflict with the local peoples caused many to fail over the years. As Maine entered the 18th century, only a half dozen European settlements survived. Patriot and British forces contended for Maine's territory during the American Revolution and the War of 1812. Maine was part of the Commonwealth of Massachusetts until 1820, when it voted to secede from Massachusetts. On March 15, 1820, it was admitted to the Union as the 23rd state under the Missouri Compromise. Maine is the 39th most extensive and the 41st most populous of the 50 United States.