311 may refer to:

  • 311 (number), a natural number
  • AD 311, a year of the Julian calendar, in the fourth century AD
  • 311 BC, a year of the pre-Julian Roman calendar
  • 311 (band), an American band
  • 311 (DSM-IV), DSM-IV code for "Depressive Disorder Not Otherwise Specified"
  • 311 Boyz, a teen gang in Las Vegas, Nevada
  • 3-1-1, the telephone number of local information service operated by some local governments in the United States and Canada
  • 3-1-1 for Carry-Ons, a procedure enacted by the United States Transportation Security Administration
  • 311 earthquake, the 2011 Tōhoku earthquake and tsunami off Japan

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