The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States. Most of its population of 6.4 million live in the Boston metropolitan area. The eastern half of this relatively small state is mostly urban and suburban. The west is primarily rural, also with most of its population in urban enclaves. Massachusetts is the most populous of the six New England states and ranks third in overall population density among the 50 states.

The first Europeans to settle New England landed in present-day Massachusetts. These settlers were primarily separatist non-conformists later called Pilgrims, and also Puritans from England seeking religious freedom. They founded Plymouth, Salem, and Boston, which soon became the hub of the region, then the Pioneer Valley along the Connecticut River where the state's best agricultural land was concentrated. A century and a half later, Massachusetts became known as the "Cradle of Liberty" for the revolutionary ferment in Boston that helped spawn the war of the Thirteen Colonies for independence.

Massachusetts was originally inhabited by several Algonquian tribes: the Wampanoag, Nauset, Nipmuc, Pocomtuc, Pennacook, Mahican, and some Narragansett and Pequot. These indigenous people were decimated by waves of smallpox inadvertently brought to the New World by Sir Herbert Popham and his ship to the Saco Maine area in 1616.

The first European settlers in Massachusetts, the Pilgrims, established their settlement at Plymouth in 1620, and developed friendly relations with the native Wampanoag. Most early settlers came from within 60 miles (100 km) of Haverhill, England. The Pilgrims were soon followed by Puritans who established the Massachusetts Bay Colony at present-day Boston. The Puritans, whose beliefs included exclusive understanding of the literal truth of the Bible, came to Massachusetts for religious freedom. Dissenters such as Anne Hutchinson, Roger Williams, and Thomas Hooker left Massachusetts because of the Puritan society's lack of religious tolerance. Williams founded the colony of Rhode Island, and Hooker founded Connecticut.

Native American-European racial tensions led to King Philip's War 1675-76. There were major campaigns in the Pioneer Valley and Plymouth Colony, as well as an unsuccessful expedition against Quebec under William Phips in 1690. Massachusetts became a single colony in 1692, the largest in New England, and one where many American institutions and traditions were formed. The colony fought alongside British regulars in a series of French and Indian Wars that were characterized by brutal border raids and successful attacks on British forces in New France (present-day Canada).

Massachusetts was a center of the movement for independence from Great Britain. With actions by patriots such as Sam Adams and John Hancock followed by counter-actions by the Crown were a main reason for the unity of the Thirteen Colonies and the outbreak of the American Revolution, starting with battles in and around Boston in 1775-76. After independence and during the formative years of independent American government, Shays' Rebellion was an armed uprising in the western half of the state from 1786 to 1787. The rebels were mostly small farmers angered by crushing war debt and taxes which resulted from their lack of representation in congress. Massachusetts was the first U.S. state to abolish slavery, in a 1783 judicial interpretation of its 1780 constitution.

On March 15, 1820, Maine separated from Massachusetts, of which it had been a non-contiguous part, and entered the Union as the 23rd State as a result of the ratification of the Missouri Compromise. Massachusetts became a national and world leader in industrialization, with its mastery of machine tools and textiles. Horace Mann made the state system of schools the national model. Henry David Thoreau and Ralph Waldo Emerson made major contributions to American thought. Members of the Trancendentalism movement, they emphasized the importance of the natural world to humanity.

In the years leading up to the Civil War, Massachusetts was a center of temperance and abolitionist activity within the United States. Antagonism to their views resulted in anti-abolitionist riots in Massachusetts between 1835 and 1837. The works of abolitionists contributed to subsequent actions of the state during the Civil War. Massachusetts was the first state to recruit, train, and arm a black regiment with white officers, the 54th Massachusetts Volunteer Infantry.

During the 19th century, the Massachusetts economy transformed from primarily agricultural to manufacturing, making use of its many rivers to power factories for shoes, furniture, and clothing that drew labor from Yankees on subsistence farms at first, and later drew upon immigrant labor from Europe. The industrial economy declined in the early twentieth century with the movement of many manufacturing companies to the southern United States, to draw upon cheaper labor. A revitalization came in the 1970s when, nourished by the graduates of the area's many elite institutions of higher education, the Boston suburbs (particularly those near Route 128) became home to dozens of high-technology companies. Massachusetts's colleges and universities, as well as its technology sectors, continue to thrive.

Massachusetts entered the twentieth century with a strong industrial economy, but by the 1920s low-wage competition from the South, followed by the Great Depression, led to the collapse of Massachusetts’ two main industries, shoes and textiles. In the years following World War II, Massachusetts was transformed from a factory system to a largely service and high-tech based economy. In the ensuing years, government contracts, private investment, and research facilities led to a new and improved industrial climate, with reduced unemployment and increased per capita income. Suburbanization flourished, as the Route 128 corridor became dotted with research developments. In 1987 the state received federal funding for the $14.6 billion Central Artery/Tunnel Project. Known colloquially as the "the Big Dig," it was at the time the biggest federal highway project ever approved.