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

  • , 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