Massachusetts (/ˌmæsəˈtʃuːsɪts/ ^ⓘ /-zɪts/ MASS-ə-CHOO-sits, -⁠zits; Massachusett: Muhsachuweesut [məhswatʃəwiːsət]), officially the Commonwealth of Massachusetts, is a state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the 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 seventh-smallest state by land area. With an estimated population of over 7.1 million, it is the most populous state in New England, the 16th-most-populous in the United States, and the third-most densely populated U.S. state, after New Jersey and Rhode Island.

Massachusetts was a site of early English colonization. The Plymouth Colony was founded in 1620 by the Pilgrims of Mayflower. In 1630, the Massachusetts Bay Colony, taking its name from the Indigenous Massachusett people, also 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. The American Revolution originated in Massachusetts, with Boston becoming known as the "Cradle of Liberty" for its political agitation. In 1786, Shays' Rebellion, a populist revolt, influenced the United States Constitutional Convention. Originally dependent on agriculture, fishing, and trade, Massachusetts transformed into a manufacturing hub during the Industrial Revolution. Before the American Civil War, the state was a center for the abolitionist, temperance, and transcendentalist movements. During the 20th century, the state's economy shifted from manufacturing to services; in the 21st century, Massachusetts has become the global leader in biotechnology, and also excels in artificial intelligence, engineering, higher education, finance, and maritime trade.

Boston is Massachusetts' capital and most populous city, as well as its cultural and financial center; other major cities are Worcester, Springfield, and Cambridge. The state also hosts the urban core of Greater Boston, the largest metropolitan area in New England, with profound influence on U.S. history, academia, and the research economy. Massachusetts has a reputation for social and political progressivism; it is the only U.S. state with a right to shelter law, and was the first U.S. state—and one of the earliest jurisdictions in the world—to legally recognize same-sex marriage. Harvard University in Cambridge is the oldest institution of higher learning in the United States, with the largest financial endowment of any university in the world. 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.

Massachusetts is the most educated U.S. state, ranking first by the percentage of population 25 and over with either a bachelor's degree or advanced degree. Its public school system ranks first in the country, with public school students placing among the top tier in the world in academic performance. Massachusetts is among the wealthiest and most developed states, with the best performing economy. It ranks first in both the American and United Nations Human Development indexes, first in per capita income, and first in median income, both by household and individually. Consequently, Massachusetts is typically recognized as the best U.S. state, as well as the most expensive state for residents to live in.

The Massachusetts Bay Colony was named after the Indigenous population, the Massachusett or Muhsachuweesut, whose name likely derived from the Wôpanâak word muswachasut, segmented as mus(ây) "big" + wach "mountain" + -s "diminutive" + -ut "locative". This word has been translated as "near the great hill", "by the blue hills", "at the little big hill", or "at the range of hills", in reference to the Blue Hills—namely, the Great Blue Hill, located on the boundary of Milton and Canton. Massachusett has also been represented as Moswetuset. This comes from the name of the Moswetuset Hummock (meaning "hill shaped like an arrowhead") in Quincy, where Plymouth Colony commander Myles Standish (a hired English military officer) and Squanto (a member of the Patuxet band of the Wamponoag people, who have since died off due to contagious diseases brought by colonists) met Chief Chickatawbut in 1621.

Although the designation "Commonwealth" forms part of the state's official name, it has no practical implications in modern times, and Massachusetts has the same position and powers within the United States as other states. John Adams may have chosen the word in 1779 for the second draft of what became the 1780 Massachusetts Constitution; unlike the word "state", the word "commonwealth" had the connotation of a republic at the time. This was in contrast to the monarchy the former colonies were fighting against during the American Revolutionary War. The name "State of Massachusetts Bay" appeared in the first draft, which was ultimately rejected. It was also chosen to include the "Cape Islands" in reference to Martha's Vineyard and Nantucket—from 1780 to 1844, they were seen as additional and separate entities confined within the Commonwealth.

Massachusetts was originally inhabited by tribes of the Algonquian language family, including the Wampanoag, Narragansett, Nipmuc, Pocomtuc, Mahican, and Massachusett. While cultivation of crops like squash and corn were an important part of their diet, the people of these tribes hunted, fished, and searched the forest for most of their food. Villagers lived in lodges called wigwams as well as longhouses. Tribes were led by male or female elders known as sachems.

In the early 1600s, European colonists caused virgin soil epidemics such as smallpox, measles, influenza, and perhaps leptospirosis in what is now known as the northeastern region of the United States. Between 1617 and 1619, a disease that was most likely smallpox killed approximately 90% of the Massachusetts Bay Native Americans.