Worcester (/ˈwʊstər/ ^ⓘ WUUST-ər, locally [ˈwɪstə] ^ⓘ) is a city in the U.S. state of Massachusetts. The principal city of Central Massachusetts, Worcester is both the second-most populous city in the state, and the 113th most populous city in the United States. Named after Worcester, England, the city had 206,518 people at the 2020 census, also making it the second-most populous city in New England, after Boston. Because it is near the geographic center of Massachusetts, Worcester is known as the "Heart of the Commonwealth"; a heart is the official symbol of the city. Worcester is the historical seat of Worcester County.

Founded in 1722 and incorporated in 1848, Worcester developed as an industrial city in the 19th century due to the Blackstone Canal and railways, which facilitated the import of raw materials and the export of such finished goods as machines, textiles, and wire. The city's population grew, driven by European immigration. After World War II, manufacturing in Worcester waned, and the city declined economically and in terms of population. This trend was not reversed until the 1990s, when higher education, medicine, biotechnology, and new immigrants started making their mark. The population has grown by 28% since 1980, reaching its all-time high in the 2020 census, in an example of urban renewal. Since the 1970s, and especially since the construction of Route 146 and interstates 90, 495, 190, 290, and 395, both Worcester and its surrounding towns have become more integrated with Boston's suburbs. The Worcester region now marks the western periphery of the Boston–Worcester–Providence (MA–RI–NH) U.S. census Combined Statistical Area (CSA), or Greater Boston.

Modern Worcester is known for its diversity and large immigrant population, with significant communities of Vietnamese, Brazilians, Albanians, Puerto Ricans, Ghanaians, Dominicans, Irish, English, Italians, Greeks, Jews and others. Twenty-two percent of Worcester's population was born outside the United States. A center of higher education, it is home to eight colleges and universities, including the College of the Holy Cross, Worcester Polytechnic Institute (WPI), Clark University, and Worcester State University. Worcester has many 19th-century triple-decker houses, Victorian-era mills and related buildings, and lunch-car diners, such as Miss Worcester.

The area was inhabited by members of the Nipmuc tribe at the time of European contact. The native people called the region Quinsigamond and built a settlement on Pakachoag Hill in Auburn.

In 1673, English settlers John Eliot and Daniel Gookin led an expedition to Quinsigamond to establish a new Christian Indian praying town and identify a new location for an English settlement. On July 13, 1674, Gookin obtained a deed to eight square miles of land in Quinsigamond from the Nipmuc people and English traders and settlers began to inhabit the region.

In 1675, King Philip's War broke out throughout New England with the Nipmuc Indians coming to the aid of Indian leader King Philip. The English settlers completely abandoned the Quinsigamond area and the empty buildings were burned by the Indian forces. The town was again abandoned during Queen Anne's War in 1702.

Finally, in 1713, Worcester was permanently resettled for a third and final time by Jonas Rice. Named after the city of Worcester, England, the town was incorporated on June 14, 1722.

On April 2, 1731, Worcester was chosen as the county seat of the newly founded Worcester County government. Between 1755 and 1758, future U.S. president John Adams worked as a schoolteacher and studied law in Worcester.