N21

N21 or N-21 may refer to:

Buses and trams

 * N21 (Long Island bus), New York
 * London Buses route N21

Roads

 * N21 road (Belgium), a National Road in Belgium
 * Route nationale 21, in France
 * N21 road (Ireland)
 * N21 (Cape Town), in South Africa
 * Nebraska Highway 21, in the United States

Other uses

 * HMS Abdiel (N21), a minelayer of the Royal Navy
 * Network TwentyOne, an Amway support organization
 * Nieuport 21, a French First World War fighter
 * Nitrogen-21, an isotope of nitrogen
 * Tumbuka language
 * N21, a postcode district in the N postcode area