Route 18 is a south–north state highway in southeastern Massachusetts.

Route 18 starts as a four-lane freeway, a continuation of John F. Kennedy Memorial Highway in downtown New Bedford, at U.S. Route 6. After the intersection with I-195, Route 18 runs via surface streets parallel to Route 140 for a while, up to a connector road with Route 140 northbound. (Before its highway route was constructed, Route 140 followed County Road from Taunton until terminating at Route 18 in Freetown near the New Bedford line.) Route 18 then continues on a generally northerly direction. The highway goes through the East Freetown section of Freetown, Lakeville (with a three-mile (5 km) concurrency with Route 105 along Assawompset Pond), Middleborough, where the highway meets U.S. Route 44 and Route 28 at the Middleboro rotary just north of Interstate 495, beginning a six-mile (10 km) concurrency with Route 28 until the center of Bridgewater, East Bridgewater, Whitman, Abington, and Weymouth, ending at Route 53.

A major fault of Route 18 north of Bridgewater is its intersection patterns. At all lights north of Bridgewater center, the road widens to four lanes temporarily, before and after the intersection. While this helps alleviate backups at the lights and assists vehicles turning left off of the route, it creates bottlenecks after the intersection, where the two lanes re-merge into one.[citation needed] To help this, the Massachusetts Department of Transportation's Highway Division will be widening the section of Route 18 From Highland Place in Weymouth to Route 139 In Abington from 2 to 4 lanes. The $26 million project is expected to begin in 2013.

The exits on the Route 18 freeway are unnumbered.

This is a listing of Route 18's intersections with numbered highways which are not located on a freeway section.