501 may refer to:

• 501, a year in the Common Era
• a year in the era B.C.
• 501, a number

Route numbers

• Ariane 5 Flight 501, a disastrous E.S.A. test flight
• List of highways numbered 501, one of a number of highways
• Pacific Western Airlines Flight 501, the flight number of an airline disaster
• 501 Queen, A streetcar route in Toronto.

Games

• 501 is the name of a game of darts
• The record score in first-class cricket by Brian Lara, and also Lara's brand of clothing in honour of this event

Military

• Avro 501, a U.K. military seaplane model
• U-501, an historic German submarine
• USS SC-501, a U.S. Coast Guard submarine chaser
• 501st Combat Support Wing, a USAFE air unit in the U.K.
• 501st Infantry Regiment (United States), the first air unit in the U.S. military
• No. 501 Squadron RAF, an historic volunteer unit of the British Air Force

Fictional Military

• 501st Legion (Star Wars), a (fictional) Imperial stormtrooper unit
  • The (real) fan group, the 501st Legion which is the namesake for the above
• 501st Joint Fighter Wing Strike Witches, a fictional unit from a Japanese anime series Strike Witches

Model numbers

• Allison 501-D, the commercial version of an aircraft turboprop model
• BMW 501, a BMW car model
• British Rail Class 501, a U.K. train model
• Fiat 501, a Fiat car model
• a type of Levi's jeans
• Nikon F501, a camera model
• Roland RE-501, an audio effects device

Other places, people, and objects

• Frenchman Butte No. 501, Saskatchewan, a rural municipality in Canada
• Nawwaf Fahd Humood Al-Otaibi, also known as Guantanamo detainee 501
• 501 Marquette, a notable building in Minneapolis, MN
• 501 Urhixidur, an asteroid
• SS501, a South Korean boyband

Other

• an HTTP status code meaning Not implemented
• SMTP Error - 501, an SMTP status code meaning Syntax error in parameters or arguments
• 501(c) is a type of tax exemption for non-profit organizations in the United States
• Area code 501, covering part of Arkansas, U.S.
• Year 501: The Conquest Continues, a book by Noam Chomsky
• the number of verbs in the 501 Verbs series from Barron's Educational Series (e.g., 501 Spanish Verbs, 501 French Verbs, etc.).
• the lowest possible VantageScore credit score, corresponding to very poor credit.