Maryland (US: MERR-il-ənd) is a state in the Mid-Atlantic region of the United States. The state borders Virginia to its south, West Virginia to its west, Pennsylvania to its north, Delaware and the Atlantic Ocean to its east, and the national capital of Washington, D.C. to the southwest. With a total area of 12,407 square miles (32,130 km²), Maryland is the ninth-smallest state by land area, and its population of 6,177,224 ranks it the 18th-most populous state and the fifth-most densely populated. Maryland's capital is Annapolis, and the most populous city is Baltimore. Occasional nicknames include Old Line State, the Free State, and the Chesapeake Bay State. It is named after Henrietta Maria, the French-born queen of England, Scotland, and Ireland during the 17th century.

Maryland's coastline was first explored by Europeans in the 16th century. Prior to that, it was inhabited by several Native American tribes, mostly the Algonquian peoples and, to a lesser degree, Iroquoians and Siouans. As one of the original Thirteen Colonies, Maryland was founded by George Calvert, 1st Baron Baltimore, a Catholic convert who sought to provide a religious haven for Catholics persecuted in England. In 1632, Charles I of England granted Lord Baltimore a colonial charter, naming the colony after his wife, Henrietta Maria. Unlike the Pilgrims and Puritans, Lord Baltimore envisioned a colony where people of different religious sects would coexist under the principle of toleration. In 1649, the Maryland General Assembly passed an Act Concerning Religion, which enshrined this principle by penalizing anyone who "reproached" a fellow Marylander based on religious affiliation. Religious strife was common in Maryland's early years, and Catholics remained a minority, albeit in greater numbers than in any other English colony. Maryland's early settlements and population centers clustered around rivers and other waterways that empty into the Chesapeake Bay. Its economy was heavily plantation-based and centered mostly on the cultivation of tobacco. Demand for cheap labor from Maryland colonists led to the importation of numerous indentured servants and enslaved Africans. In 1760, Maryland's current boundaries took form following the settlement of a long-running border dispute with Pennsylvania. Maryland was an active participant in the events leading up to the American Revolution, and in 1776, its delegates to the Second Continental Congress in Philadelphia signed the Declaration of Independence. Many of its citizens subsequently played key political and military roles in the American Revolutionary War. Although it was a slave state, Maryland remained in the Union during the American Civil War, and its strategic location made it a significant strategic location during the war. After the Civil War ended, Maryland took part in the Industrial Revolution, driven by its seaports, railroad networks, and mass immigration from Europe.

Since the 1940s, the state's population has grown rapidly, to approximately six million residents, and it is among the most densely populated U.S. states. As of 2015, Maryland had the highest median household income of any state, owing in large part to its proximity to Washington, D.C., and a highly diversified economy spanning manufacturing, retail services, public administration, real estate, higher education, information technology, defense contracting, health care, and biotechnology. Maryland is one of the most multicultural states in the country; it is one of the six states where non-Whites compose a majority of the population, with the fifth-highest percentage of African Americans, and high numbers of residents born in Africa, Asia, Central America, and the Caribbean. The state's central role in U.S. history is reflected by its hosting of some of the highest numbers of historic landmarks per capita.

The western portion of the state contains numerous stretches of the Appalachian Mountains, the central portion is primarily composed of the Piedmont, and the eastern side of the state makes up a significant portion of Chesapeake Bay. Sixteen of Maryland's twenty-three counties, and the city of Baltimore, border the tidal waters of the Chesapeake Bay estuary and its many tributaries, which combined total more than 4,000 miles of shoreline. Although one of the smallest states in the U.S., it features a variety of climates and topographical features that have earned it the moniker of America in Miniature. In a similar vein, Maryland's geography, culture, and history combine elements of the Mid-Atlantic, Northeastern, and Southern regions of the country.