New Hampshire Route 108 (abbreviated NH Route 108 or NH 108) is a 42.42-mile (68.27 km) long north–south state highway in Rockingham and Strafford counties in southeastern New Hampshire. The northern terminus of the route is in the city of Rochester at NH Route 125 and NH Route 202A. The southern terminus is at the Massachusetts state line in the town of Plaistow, where NH 108 continues south as Massachusetts Route 108 for 0.91 miles (1.46 km) to Massachusetts Route 110 in the city of Haverhill.

NH 108 is notable in being one of two routes (the other being NH 9) to intersect both U.S. Route 4 and NH Route 4 (a rare case of two completely separate routes in one state having the same number).

NH 108 begins at the border between Haverhill, Massachusetts, and Plaistow, New Hampshire, as a continuation of Massachusetts Route 108, which passes under Interstate 495 just south of the state line before ending at Massachusetts Route 110, which heads east as Amesbury Road and west into downtown Haverhill as Kenoza Avenue. NH 110 passes through the town of Plaistow before crossing through Newton into East Kingston and crossing NH 107A. The route continues north, before turning eastward to form a brief wrong-way concurrency with NH 107, and turning back to the north. NH 108 next passes through the town of Kensington, where it meets the north end of NH 150 and then continues north into the town of Exeter. In Exeter, NH 108 meets NH 27, NH 111, and NH 111A, forming a very brief overlap with the former two routes. The route then meets the west end of Route 88 and then promptly interchanges with the Route 101 freeway at Exit 11.

Route 108 continues north into the town of Stratham where it meets NH 33, a connector to U.S. Route 1 in Portsmouth which also interchanges with Interstate 95. Continuing northward, NH 108 passes through the towns of Newfields and Newmarket, intersecting with NH 85 and NH 152. The road then crosses into Strafford County and into the town of Durham. NH 108 passes through the center of town, just east of the University of New Hampshire main campus, and then interchanges with U.S. Route 4. Route 108 passes through eastern Madbury with no route intersections, and then makes its way into the city of Dover.

After crossing into Dover, NH 108 interchanges with the Spaulding Turnpike (NH 16) at Exit 7. Shortly thereafter, the road comes to an intersection with NH 9 and NH 4, which begins here. The three routes briefly run concurrently in the center of Dover, before NH 4 splits off towards South Berwick, Maine via Portland Avenue. NH 9 and NH 108 continue north until NH 9 splits off towards Berwick, Maine, near an intersection with the Spaulding Turnpike at Exit 9 (via Indian Brook Road westbound). NH 108 continues north into the city limits of Somersworth, where it meets NH 236, a short connector to NH 9 bound for Berwick and, ultimately, Kittery, Maine. Continuing northbound, NH 108 roughly parallels the Spaulding Turnpike, crossing into Rochester, before ending at an intersection with NH 125 and NH 202A in the center of the city. From the northern end of NH 108, one may turn left or right onto Columbus Avenue, which carries NH 125, or continue straight onto North Main Street (NH 202A westbound).