401 may refer to:

• 401 (number), the natural number following 400 and preceding 402
• A year: 401 BC or AD 401
• Ontario Highway 401, a highway that extends across Southern Ontario, Canada
  • There are also other roads named 401, see the List of highways numbered 401
• 401(a), a type of U.S. tax-deferred retirement savings plan defined by a subsection of the Internal Revenue Code
• 401(k), a type of U.S. employer-sponsored retirement plan defined by a subsection of the Internal Revenue Code
• Bristol 401, a car produced by Bristol Cars in the early 1950s
• HTTP 401, a status in the HTTP protocol indicating authentication has failed
• .401 Winchester Self-Loading centerfire rifle cartridge introduced in 1910
• Area code 401
• Cessna 401, an airplane