New Hampshire Route 12 is a north-south state highway running across the western portion of New Hampshire from the Massachusetts state line to the Vermont state line at the Connecticut River.

Route 12 begins at the Massachusetts state line in Fitzwilliam. It goes through Keene, then travels along the east bank of the Connecticut River until Claremont. From there, it crosses the Connecticut River into Vermont.

New Hampshire Route 12A is a designation held by two separate state highways in the U.S. state of New Hampshire. Although not directly connected, the two segments are linked by a 9-mile (14 km) section of New Hampshire Route 12.

The southern segment of NH 12A is a 21.56-mile (34.70 km) long loop route that runs southwest and south from Charlestown to Keene. The northern terminus is at NH 12 south of Charlestown. The southern terminus is at an interchange with NH 12 northwest of Keene.

The northern segment of NH 12A is a 26.89-mile (43.28 km) long spur route that runs north–south along the eastern side of the Connecticut River. The northern terminus is at U.S. Route 4 and New Hampshire Route 10 in West Lebanon. The southern terminus is at NH 12 north of Charlestown.