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 (album), band 311's self-titled album
311 (DSM-IV), DSM-IV code for "Depressive Disorder Not Otherwise Specified"
311 Boyz, a teen gang in Las Vegas, Nevada
311 Claudia, a main-belt asteroid
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
311, the area code of a common fictitious telephone number (311-555-2368) used in early Bell System ads and in fiction