Cambridge is noted for its diverse population, both racially and economically. Residents, known as Cantabrigians, range from affluent MIT and Harvard professors to working-class families to immigrants. The first legal same-sex civil marriage ceremonies in America were held at Cambridge's City Hall.

The city and its universities, particularly Harvard, have strong leftist traditions, with some even referring to the city as the PRC, or the "People's Republic of Cambridge" and Harvard as the Kremlin on the Charles. Cambridge is also known as "Boston's Left Bank".

Cambridge has also been called the "City of Squares" by some, as most of its commercial districts are major street intersections known as squares. Because most streets were laid out centuries ago, many streets such as those surrounding the Cambridge Common are still in the shape of the original cattle-paths leading from the "green" towards the general direction the cattle used to head home. Few of these squares in Cambridge actually resemble a geometric square in any way—Harvard Square is in fact formed by two converging curved streets. Each of the squares acts as something of a neighborhood center. These include:

Kendall Square, formed by the junction of Broadway, Main Street, and Third Street. Just over the Longfellow Bridge from Boston, at the eastern end of the MIT campus. It is served by an MBTA Red Line station. Most of Cambridge's large office towers are located here, giving the area somewhat of an office park feel. A flourishing biotech industry has grown up around here. The "One Kendall Square" complex is nearby, but—confusingly—not actually in Kendall Square.

Central Square, formed by the junction of Massachusetts Avenue, Prospect Street, and Western Avenue. This is perhaps the closest thing Cambridge has to a downtown, and is well-known for its wide variety of ethnic restaurants. Even as recently as the late 1990s it was rather run-down; it underwent a controversial gentrification in recent years (in conjunction with the development of the nearby University Park at MIT), and continues to grow more expensive. It is served by a Red Line station. Lafayette Square, formed by the junction of Massachusetts Avenue, Columbia Street, Sidney Street, and Main Street, is considered a part of the Central Square area. Cambridgeport is south of Central Square along Western Avenue and River Street.

Harvard Square, formed by the junction of Mass. Avenue, Brattle Street, and JFK Street. This is the site of Harvard University, the oldest university in the United States and is a major Cambridge shopping area (although not as exclusively so as in years past). It is served by a Red Line station. A short distance away from the square lies the Cambridge Common, while the neighborhood north of Harvard but east of Mass Ave is known as Agassiz in honor of the famed scientist Louis Agassiz.

Porter Square, about a mile north on Mass. Ave from Harvard Square, formed by the junction of Mass. Ave and Somerville Ave, and including part of the city of Somerville. It is served by the Porter Square station which includes a Red Line stop and a Fitchburg Line commuter rail stop in the same building.

Inman Square, at the junction of Cambridge and Hampshire streets in Mid-Cambridge. The most "funky" and "unique" of the squares, Inman Square is home to many diverse restaurants, bars and boutiques. Ryles Jazz Club and the S&S Deli are two legends of Inman Square. The funky street scene still holds some urban flair but was dressed up recently with victorian street lights, benches and bus-stops. A new community park was installed and is a favorite place to enjoy some takeout food from the nearby restaurants and ice cream parlor.

Lechmere Square, at the junction of Cambridge and First streets, adjacent to the CambridgeSide Galleria shopping mall. Perhaps best known as the eastern terminus of the MBTA Green Line subway.

Cambridgeport, between Mass Ave and the Charles River, from Central Square to MIT

Riverside, south of Massachusetts Avenue to the Charles River between Central and Harvard Squares

Area 4, between Cambridgeport, Mid-Cambridge, and East Cambridge

Wellington-Harrington, opposite Hampshire Street from Area4, to the Somerville border

East Cambridge

North Cambridge

Agassiz

Avon Hill

Mid Cambridge, bounded by Central, Harvard, Inman Squares, and the City of Somerville.

Brattle Street

West Cambridge

Strawberry Hill

Cambridge was established as the town of "Newtowne" in 1630. Newtowne was one of a number of towns (including Boston, Dorchester, Watertown, and Weymouth) founded by the 700 original Puritan colonists of the Massachusetts Bay Colony under governor John Winthrop. The original village site was the heart of today's Harvard Square, while the town included a much larger area than the present city, with various outlying parts becoming independent towns over the years: Newton (originally Newtown) in 1690, Lexington (Cambridge Farms) in 1712, and Arlington (West Cambridge) and Brighton (Little Cambridge), which has since been annexed by Boston, in 1807

In 1636 Harvard College was founded by the colony to train ministers and Newtowne was chosen for its site. In 1638 the name was changed to "Cambridge" (after Cambridge, England) to reflect its status as the center for higher education in the colony.

Cambridge grew slowly as an agricultural village eight miles by road from Boston, the capital of the colony. By the American Revolution, most residents lived near the Common and Harvard College, with farms and estates comprising most of the town. Most of the inhabitants were descendants of the original Puritan colonists, but there was also a small elite of Anglicans "worthies" who were not involved in village life, made their livings from estates, investments, and trade, and lived in mansions along "the Road to Watertown" (today's Brattle Street), which is known as Tory Row. Most of these estates were confiscated after the revolution and sold to Loyalists.

Between 1790 and 1840, Cambridge began to grow rapidly with the construction of the West Boston Bridge in 1792 that connected Cambridge directly to Boston, making it no longer necessary to travel eight miles through the Boston Neck, Roxbury, and Brookline to cross the Charles River. A second bridge, the Canal Bridge, opened in 1809 alongside the new Middlesex Canal. The new bridges and roads made what were formerly estates and marshland prime industrial and residential districts. Soon after, turnpikes were built: the Concord Turnpike (today's Broadway and Concord Ave.), the Middlesex Turnpike (Hampshire St. and Massachusetts Ave. northwest of Porter Square), and what are today's Cambridge, Main, and Harvard Streets were roads to connect various areas of Cambridge to the bridges. In addition, railroads crisscrossed the town during the same era, leading to the development of Porter Square as well as the creation of neighboring town Somerville from the formerly rural parts of Charlestown.

Cambridge was incorporated as the second city in Massachusetts in 1846. Its commercial center also began to shift from Harvard Square to Central Square, which became the downtown of the city. Between 1850 and 1900, Cambridge took on much of its present character — streetcar suburban development along the turnpikes, with working-class and industrial neighborhoods focused on East Cambridge, comfortable middle-class housing being built on old estates in Cambridgeport and Mid-Cambridge, and upper-class enclaves near Harvard University and on the minor hills of the city. The coming of the railroad to North Cambridge and Northwest Cambridge then led to three major changes in the city: the development of massive brickyards and brickworks between Massachusetts Ave., Concord Ave. and Alewife Brook; the ice-cutting industry launched by Frederic Tudor on Fresh Pond; and the carving up of the last estates into residential subdivisions to provide housing to the thousands of immigrants that moved to work in the new industries.

By 1920, Cambridge was one of the main industrial cities of New England with nearly 120,000 residents. As industry in New England began to decline during the Great Depression and after World War II, Cambridge lost much of its industrial base. It also began the transition to being an intellectual, rather than an industrial, center. Harvard University had always been important in the city (both as a landowner and as an institution), but began to play a more dominant role in the city's life and culture. Also, the move of the Massachusetts Institute of Technology from Boston in 1912 ensured Cambridge's status as an intellectual center of the United States.

After the 1950s, the city population began to decline slowly, as families were replaced by single people and young couples, and by the end of the twentieth century, Cambridge had one of the most expensive housing markets in the Northeastern United States. While maintaining much diversity in class, race, and age, it became harder and harder for those who grew up in the city to be able to afford to stay. As of 2006, while the Cambridge real estate market is widely considered to be overvalued, its mix of amenities and proximity to Boston have kept housing prices relatively stable.