The Housatonic River is a river, approximately 144 mi (230 km) long, in western Massachusetts and central Connecticut in the United States. It drains an area of southwestern New England into Long Island Sound. Its watershed is just to the west of the watershed of the lower Connecticut River.

It rises in far western Massachusetts in the Berkshire Mountains near the city of Pittsfield. It flows southward through western Massachusetts through the Berkshires and into western Connecticut. It empties into Long Island Sound in a fjord near the town of Stratford.

It receives the Naugatuck River at Derby, Connecticut. It receives the Still River south of New Milford, Connecticut. The river is impounded in several places in Connecticut for hydroelectricity.

Until 1977 the river received PCB pollution from the General Electric plant at Pittsfield. Although the water quality has improved in recent decades, the river continues to be contaminated by PCBs.

Inspired by the river during his honeymoon, the American classical music composer Charles Ives wrote The Housatonic at Stockbridge as part of his composition Three Places in New England.

• List of Connecticut rivers
• List of Massachusetts rivers

• Housatonic River Initiativer-Riverkeeper
• Housatonic River Restoration
• Charles Ives' Three Places in New England