Cambridge (/ˈkeɪmbrɪdʒ/ KAYM-brij) is a city in Middlesex County, Massachusetts, United States. It is a suburb in the Greater Boston metropolitan area, located directly across the Charles River from Boston. The city's population as of the 2020 U.S. census was 118,403, making it the most populous city in the county, the fourth-largest in Massachusetts behind Boston, Worcester, and Springfield, and ninth-most populous in New England. The city was named in honor of the University of Cambridge in Cambridge, England, which was an important center of the Puritan theology that was embraced by the town's founders.

Founded in December 1630 during the colonial era, Cambridge was one among the first cities established in the Thirteen Colonies, and it went on to play a historic role during the American Revolution. In May 1775, approximately 16,000 American patriots assembled in Cambridge Common to begin organizing a military retaliation against British troops following the Battles of Lexington and Concord. On July 2, 1775, two weeks after the Second Continental Congress in Philadelphia formally established the Continental Army and appointed George Washington commander of it, Washington arrived at Cambridge Common to take command of the Patriot soldiers camped there. Many of these soldiers played a role in supporting Washington's successful siege of Boston, which trapped garrisoned British troops from moving by land, forcing the British to ultimately abandon Boston. Cambridge Common is thus celebrated as the birthplace of the Continental Army.

Harvard University, an Ivy League university founded in Cambridge in 1636, is the oldest institution of higher learning in the United States. The Massachusetts Institute of Technology (MIT), Lesley University, and Cambridge College also are based in Cambridge. Radcliffe College, a women's liberal arts college, was based in Cambridge from its 1879 founding until its assimilation into Harvard in 1999.

Kendall Square, near MIT in the eastern part of Cambridge, has been called "the most innovative square mile on the planet" due to the high concentration of startup companies that have emerged there since 2010. In 2022, Cambridge was home to over 250 biotech companies, with more than 120 located within the Kendall Square zipcode.

The Massachusett inhabited the area that is now called Cambridge for thousands of years prior to European colonization of the Americas, most recently under the name Anmoughcawgen, which means 'fishing weir' or 'beaver dam' in Natick. At the time of European contact, the area was inhabited by Naumkeag or Pawtucket to the north and Massachusett to the south, and may have been inhabited by other groups such as the Totant, not well described in later European narratives. The contact period introduced a number of European infectious diseases which would decimate native populations in virgin soil epidemics, leaving the area uncontested upon the arrival of large groups of English settlers in 1630.

The first settlement of the Massachusetts Bay Colony was established in Salem, in June of 1630. That December, the site of present-day Cambridge was chosen for development because it was safely upriver from Boston Harbor, making it easily defensible from attacks by enemy ships. The city was founded by Thomas Dudley, his daughter Anne Bradstreet, and his son-in-law Simon Bradstreet. The first houses were built in the spring of 1631. The settlement was initially referred to as "the newe towne". Official Massachusetts records show the name rendered as Newe Towne by 1632, and as Newtowne by 1638.

Located at the first convenient Charles River crossing west of Boston, Newtowne was one of several towns, including Boston, Dorchester, Watertown, and Weymouth, founded by the 700 original Puritan colonists of the Bay Colony under Governor John Winthrop. Its first preacher was Thomas Hooker, who led many of its original inhabitants west in 1636 to found Hartford and the Connecticut Colony; before leaving, they sold their plots to more recent immigrants from England. The original village site is now within Harvard Square. The marketplace where farmers sold crops from surrounding towns at the edge of a salt marsh (since filled) remains within a small park at the corner of John F. Kennedy and Winthrop Streets.

In 1636, Newe College, later renamed Harvard College after benefactor John Harvard, was founded as North America's first institution of higher learning. Its initial purpose was training ministers. According to Cotton Mather, Newtowne was chosen for the site of the college by the Great and General Court, then the legislature of the Massachusetts Bay Colony, primarily for its proximity to the popular and highly respected Puritan preacher Thomas Shepard. In May 1638, the settlement's name was changed to Cambridge in honor of the University of Cambridge in Cambridge, England.