Delaware ( DEL-ə-wair) is a state in the Mid-Atlantic region of the United States. It borders Maryland to its south and west, Pennsylvania to its north, New Jersey to its northeast, and the Atlantic Ocean to its east. The state's name derives from the adjacent Delaware Bay, which in turn was named after Thomas West, 3rd Baron De La Warr, an English nobleman and the Colony of Virginia's first colonial-era governor.

Delaware occupies the northeastern portion of the Delmarva Peninsula, and some islands and territory within the Delaware River. It is the 2nd smallest and 6th least populous state, but also the 6th most densely populated. Delaware's most populous city is Wilmington, and the state's capital is Dover, the 2nd most populous city in Delaware. The state is divided into three counties, the fewest number of counties of any of the 50 U.S. states; from north to south, the three counties are: New Castle County, Kent County, and Sussex County.

The southern two counties, Kent and Sussex counties, historically have been predominantly agrarian economies. New Castle is more urbanized and is considered part of the Delaware Valley metropolitan statistical area that surrounds and includes Philadelphia, the nation's 6th most populous city. Delaware is considered part of the Southern United States by the U.S. Census Bureau, but the state's geography, culture, and history are a hybrid of the Mid-Atlantic and Northeastern regions of the country.

Before Delaware coastline was explored and developed by Europeans in the 16th century, the state was inhabited by several Native Americans tribes, including the Lenape in the north and Nanticoke in the south. The state was first colonized by Dutch traders at Zwaanendael, near present-day Lewes, Delaware, in 1631.

Delaware was one of the Thirteen Colonies that participated in the American Revolution and American Revolutionary War, in which the American Continental Army, led by George Washington, defeated the British, ended British colonization and established the United States as a sovereign and independent nation.

On December 7, 1787, Delaware was the first state to ratify the Constitution of the United States, earning it the nickname "The First State".

Since the turn of the 20th century, Delaware has become an onshore corporate haven whose corporate laws are deemed appealing to corporations; over half of all New York Stock Exchange-listed corporations and over three-fifths of the Fortune 500 are legally incorporated in the state.

Currently, 46th U.S. president Joe Biden is the first holder of that office to be from Delaware.