Massachusetts ( (listen), ; Massachusett: Muhsachuweesut /məhswatʃəwiːsət/), officially the Commonwealth of Massachusetts, is the most populous state in the New England region of the Northeastern United States, exceeding 7 million residents at the 2020 United States census, its highest decennial count ever. The state borders the Atlantic Ocean and Gulf of Maine to its east, Connecticut and Rhode Island to its south, New Hampshire and Vermont to its north, and New York to its west. Massachusetts is the 6th smallest state by land area but is the 15th most populous state and the 3rd most densely populated, after New Jersey and Rhode Island. The state's capital and most populous city, as well as its cultural and financial center, is Boston. Massachusetts is also home to the urban core of Greater Boston, the largest metropolitan area in New England and a region profoundly influential upon American history, academia, and the research economy. Originally dependent on agriculture, fishing, and trade, Massachusetts was transformed into a manufacturing center during the Industrial Revolution. During the 20th century, Massachusetts's economy shifted from manufacturing to services. Modern Massachusetts is a global leader in biotechnology, engineering, higher education, finance, and maritime trade.

Massachusetts was a site of early English colonization: the Plymouth Colony was founded in 1620 by the Pilgrims of the Mayflower, and in 1630 the Massachusetts Bay Colony, taking its name from the indigenous Massachusett people, established settlements in Boston and Salem. In 1692, the town of Salem and surrounding areas experienced one of America's most infamous cases of mass hysteria, the Salem witch trials. In 1777, General Henry Knox founded the Springfield Armory, which, during the Industrial Revolution, catalyzed numerous important technological advances, including interchangeable parts. In 1786, Shays' Rebellion, a populist revolt led by disaffected American Revolutionary War veterans, influenced the United States Constitutional Convention. In the 18th century, the Protestant First Great Awakening, which swept Britain and the Thirteen Colonies, originated from the pulpit of Northampton preacher Jonathan Edwards. In the late 18th century, Boston became known as the "Cradle of Liberty" for the agitation there that later led to the American Revolution.

Massachusetts has played a powerful scientific, commercial, and cultural role in the history of the United States. Before the American Civil War, Massachusetts was a center for the abolitionist, temperance, and transcendentalist movements. In the late 19th century, the sports of basketball and volleyball were invented in the western Massachusetts cities of Springfield and Holyoke, respectively. Massachusetts became the first U.S. state and one of the earliest jurisdictions in the world to legally recognize same-sex marriage as a result of the Massachusetts Supreme Judicial Court's decision in Goodridge v. Department of Public Health in 2004, and Boston is considered a hub of LGBT culture and LGBT activism in the United States. Prominent American political dynasties have hailed from the state, including the Adams and Kennedy families.

Harvard University in Cambridge is the oldest institution of higher learning in the United States, with the largest financial endowment of any university. The university has educated eight Presidents of the United States while Harvard Law School has educated a contemporaneous majority of Justices of the Supreme Court of the United States. Kendall Square in Cambridge has been called "the most innovative square mile on the planet", in reference to the high concentration of entrepreneurial start-ups and quality of innovation which have emerged in the vicinity of the square since 2010. Both Harvard and MIT, also in Cambridge, are perennially ranked as either the most or among the most highly regarded academic institutions in the world. The state's public-school students place among the top tier in the world in academic performance. Massachusetts has been ranked as one of the top states in the United States for citizens to live in, as well as one of the most expensive.

Massachusetts is one of the most educated, developed, and wealthiest states; ranking 1st in percentage of population 25 and over with a bachelor's degree and 1st in percentage of population 25 and over with an advanced degree, 1st on both the American Human Development Index and the standard Human Development Index, 1st in per capita income and 2nd in median household income.