Lyman is a town in Grafton County, New Hampshire, United States.

Until 1854, Lyman included the land which is now Monroe, New Hampshire, but it was split due to the difficulty in traversing Gardner Mountain which formerly bisected the town.

The highest point in town is 2,285 feet (696 m) above sea level, just east of the summit of Signal Mountain, a knob along the ridge of Gardner Mountain, which defines the town's western boundary.

The town's initial grant included land along the Connecticut River.

In 1854 the portion of Lyman found west of "Gardner's Mountain" was separately incorporated as Monroe.