Greenfield is the county seat, and sole city, of Franklin County, Massachusetts, United States. Greenfield was first settled in 1686. The population was 17,768 at the 2020 census. Greenfield is home to Greenfield Community College, the Pioneer Valley Symphony Orchestra, the Franklin County Fair, and the Green River Festival. The city has a Main Street Historic District containing fine examples of Federal, Greek Revival, and Victorian architecture.

Greenfield anchors the Greenfield Town, MA Micropolitan Statistical Area, which is included in the Springfield-Greenfield Town, MA Combined Statistical Area.

Pocumtuck Indians first settled and originally inhabited the Greenfield area. Native American artifacts found in the area have been dated between 7,000 and 9,000 BCE. The Pocumtucks planted field crops and fished local rivers. Some sources claim that they were wiped out by the Mohawks in 1664 and that the land was left unoccupied. Other sources show that the Pocumtucks joined the Wampanoag chief Metacom in August 1675 in the fight against English encroachment, indicating a continued presence in the area. The Pocumtuck also played an important role in the Battle of Turner's Falls on May 19, 1676, and tribal oral tradition indicates that following the battle, elements of the Pocumtuck fled to and were incorporated into the Abenaki people to the north and the Mahican people to the west.

The area was colonized as part of Deerfield by the English in 1686. In 1753, Greenfield, named for the Green River, was incorporated as a separate town from Deerfield.

In 1795, the South Hadley Canal opened, enabling boats to bypass the South Hadley falls and reach Greenfield via the Connecticut River. Located at the confluence of the Deerfield and Green rivers, and not far from where they merge into the Connecticut River, Greenfield developed into a trade center. Falls provided water power for industry, and Greenfield grew into a prosperous mill town. John Russell established the Green River Works in 1834, hiring skilled German workers at what was the country's first cutlery factory. The Connecticut River Railroad was the first of several railways to enter the town, replacing the former canal trade. During the 19th and 20th centuries, Greenfield was one of the most important American centers of the tap and die business and was the home of Greenfield Tap & Die Company (GTD).

It was designated the county seat when Franklin County was created from Hampshire County in 1811.

According to the United States Census Bureau, the town has a total area of 22 square miles (56.7 km²), of which 21 square miles (55.5 km²) is land and 0.5 square miles (1.2 km²), or 2.08%, is water. Greenfield is located at the center of the county and is bordered by Colrain, Leyden, and Bernardston to the north; Gill to the east; Montague to the southeast; Deerfield to the south; and Shelburne to the west. Greenfield is located 39 miles (63 km) north of Springfield and 90 miles (145 km) west-northwest of Boston.

Greenfield lies at the confluence of the Deerfield, Green, and Connecticut rivers. The Green River runs from the north, through town to the Deerfield, which lies along the city's southern border. From there, the Deerfield meets the Connecticut, which flows southward along the Montague border before bending eastward briefly before continuing southward. Several brooks flow into the three rivers, as well as a fourth river, the Fall River, which makes up the city's border with Gill. The city is located beside the Pocumtuck Range, the northernmost subridge of the Metacomet Ridge, and is surrounded by hills, with the town center lying on an elevated point above the rivers.