The N81 road is a national secondary road in Ireland, from the M50 motorway to Tullow, County Carlow, north to south. The N81 continues past Tullow for another 8 km to terminate at the village of Closh, County Carlow, where it intersects the N80. The N81 is 76.784 km (47.711 mi) long. The road is a dual carriageway between M50 motorway and west of Tallaght, known as the Tallaght Bypass or Blessington Road. It intersects with the M50 motorway at Junction 11. There are plans to extend the dual carriageway by 5 km (3.1 mi) to the urban boundary.

A national secondary road is a category of road in Ireland. These roads form an important part of the national route network but are secondary to the main arterial routes which are classified as national primary roads. National secondary roads are designated with route numbers higher than those used for primary roads, but with the same "N" prefix. Routes N51 and higher are all national secondary roads.