Monhegan (/mɒnˈhiːɡən/ mon-HEE-gən) is a historic island plantation in the Gulf of Maine, approximately 12 nautical miles (22 km; 14 mi) off the coast of Maine. Part of Lincoln County, Maine, the island has been inhabited for over 400 years and is renowned as one of America's oldest and most influential artist colonies. With a year-round population of 64 as of the 2020 census, Monhegan fishermen manage Maine's only lobster conservation area.

The island's dramatic landscape of towering cliffs, pristine forests, and rugged coastline has attracted artists, writers, and naturalists for more than a century. Notable artists including Edward Hopper, George Bellows, Rockwell Kent, Jay Hall Connaway, and Jamie Wyeth have found inspiration on its shores. Designated as a National Natural Landmark in 1966 for its exceptional coastal and island flora, Monhegan represents one of the best-preserved island ecosystems in the North Atlantic.

The plantation comprises Monhegan Island proper and the smaller neighboring Manana Island, together forming a unique maritime community that balances historical preservation, environmental conservation, and sustainable tourism. Access is limited to scheduled ferry service from Boothbay Harbor, New Harbor, and Port Clyde, helping preserve the island's distinctive character and fragile ecosystem. Visitors' cars are not permitted on the island, maintaining its historic character and environmental integrity.

The name Monhegan is a corruption of Monchiggon, the Abenaki language term for "out-to-sea island" used by Samoset, an Abenaki sagamore and the first Native American to make contact with the Pilgrims of Plymouth Colony, in his early contacts with the English. European explorers Martin Pring visited in 1603, Samuel de Champlain in 1604, George Weymouth in 1605 and Captain John Smith in 1614. The island got its start as a British fishing camp prior to settlement of the Plymouth Colony. Cod was harvested from the rich fishing grounds of the Gulf of Maine, then dried on fish flakes before shipment to Europe. A trading post was built to conduct business with the Indians, particularly in the lucrative fur trade. It was Monhegan traders who taught English to Samoset, the chieftain who in 1621 startled the Pilgrims by boldly walking into their new village at Plymouth and saying: "Welcome, Englishmen." On 28 January 1623 the Council for New England issued a commission for seizing the "Island of Mannahigan". Settlement by William Vengham and William Pomfret in 1623 caused William Bradford to include Monhegan among places that experienced "scattered beginnings" that year.

On April 29, 1717, Monhegan was visited by the Anne, a small square-rigged snow crewed by pirates. She had originally been captured off the Virginia Capes in April by the pirate Samuel Bellamy in the Whydah, which wrecked in a storm on the night of April 26, 1717, off Cape Cod. The Anne made it through the storm with another captured vessel, the Fisher (which was soon abandoned and the pirates aboard her transferred to the Anne). The pirates, led by Richard Noland, arrived at Monhegan on April 29, and waited for the Whydah, for the pirates had not seen or heard about the Whydah wrecking in the storm of the night of April 26. The pirates eventually realized the Whydah was lost, and proceeded to attack vessels at Matinicus Island and Pemaquid (now Bristol). They outfitted for their own uses a small 25-ton sloop belonging to Colonel Stephen Minot they had captured off Matinicus. They abandoned all the other captured vessels (including the Anne) and most of their prisoners at Matinicus on or about May 9, 1717, on Minot's sloop.

Despite success as a fishing and trade center, Monhegan would be caught in the conflict between New England and New France for control of the region. During King Philip's War (1675-1678), dispossessed English settlers from the mainland sought refuge on the island before being relocated elsewhere along the coast. During King William's War (1688-1697), the island was captured for the Kingdom of France in 1689 by Baron de Saint-Castin. He destroyed the fishing fleet and burned the buildings, with many inhabitants escaping to Massachusetts. But even during periods when Monhegan was abandoned, its convenient offshore harbor remained a stopover destination for ships. The end of the French and Indian War in 1763 brought peace to the area, and on September 4, 1839, Mohegan—again under English Colonial control—was incorporated as an island plantation.

In 1824, a conical stone lighthouse was built on the island by order of Congress and President James Monroe. Damaged by storms, it was replaced in 1850 by the present 48 foot (14.6 m) granite tower, with a fog bell station built in 1855 on nearby Manana Island. The island's 1,000 acres (400 ha) of good land encouraged agriculture, with potatoes the chief crop. But fishing was always the most important industry, whether locally or at the Grand Banks. Today, it still dominates Monhegan's economy. From October 1 through June, fishermen harvest lobsters from the only lobster conservation area in the state of Maine.

Henry Trefethen was one of the original purchasers of Monhegan Island. The Trefethen House, the oldest house on Monhegan Island, served as a hotel for island visitors, and remains standing today.