Connecticut ( kə-NET-ik-ət) is a state in the New England region of the Northeastern United States. It borders Rhode Island to the east, Massachusetts to the north, New York to the west, and Long Island Sound to the south. Its capital is Hartford, and its most populous city is Bridgeport. Connecticut lies between the major hubs of New York City and Boston along the Northeast Corridor, where the New York-Newark Combined Statistical Area, which includes four of Connecticut's seven largest cities, extends into the southwestern part of the state. Connecticut is the third-smallest state by area after Rhode Island and Delaware, and the 29th most populous with slightly more than 3.6 million residents as of 2020, ranking it fourth among the most densely populated U.S. states.

The state is named after the Connecticut River, the longest in New England, which roughly bisects the state and drains into the Long Island Sound between the towns of Old Saybrook and Old Lyme. The name of the river is in turn derived from anglicized spellings of Quinnetuket, a Mohegan-Pequot word for "long tidal river". Before the arrival of the first European settlers, the region was inhabited by various Algonquian tribes. In 1633, the Dutch West India Company established a small, short-lived settlement called House of Hope in Hartford. Half of Connecticut was initially claimed by the Dutch colony New Netherland, which included much of the land between the Connecticut and Delaware Rivers, although the first major settlements were established by the English around the same time. Thomas Hooker led a band of followers from the Massachusetts Bay Colony to form the Connecticut Colony, while other settlers from Massachusetts founded the Saybrook Colony and the New Haven Colony; both merged into the former by 1664.

Connecticut's official nickname, the "Constitution State", refers to the Fundamental Orders adopted by the Connecticut Colony in 1639, which is considered by some to be the first written constitution in Western history. As one of the Thirteen Colonies that rejected British rule during the American Revolution, Connecticut was influential in the development of the federal government of the United States. In 1787, Roger Sherman and Oliver Ellsworth, state delegates to the Constitutional Convention, proposed a compromise between the Virginia and New Jersey Plans; its bicameral structure for Congress, with a respectively proportional and equal representation of the states in the House of Representatives and Senate, was adopted and remains to this day. In January 1788, Connecticut became the fifth state to ratify the Constitution.

Connecticut is a developed and affluent state, performing well on the Human Development Index and on different metrics of income except for equality. It is home to a number of prestigious educational institutions, including Yale University in New Haven, as well as other liberal arts colleges and private boarding schools in and around the "Knowledge Corridor". Due to its geography, Connecticut has maintained a strong maritime tradition; the United States Coast Guard Academy is located in New London by the Thames River. The state is also associated with the aerospace industry through major companies Pratt & Whitney and Sikorsky Aircraft headquartered in East Hartford and Stratford, respectively. Historically a manufacturing center for arms, hardware, and timepieces, Connecticut, as with the rest of the region, had transitioned into an economy based on the financial, insurance, and real estate sectors; many multinational firms providing such services can be found concentrated in the state capital of Hartford and along the Gold Coast in Fairfield County.