121

121 may refer to:

• 121 (number), a natural number
• AD 121, a year in the 2nd century AD
• 121 BC, a year in the 2nd century BC

• 121 (Eagle) Sqn, a Royal Air Force aircraft squadron that during the Second World War was one of the three Eagle Squadrons manned by American volunteers
• 121 (MBTA bus), a Massachusetts Bay Transport Authority bus route
• 121 (New Jersey bus), a New Jersey Transit bus route
• Road 121, see list of highways numbered 121
• Russian cruiser Moskva (pennant number: 121)
• "121", a song by Robert Forster from the album Calling from a Country Phone
• 121 Hermione, a main-belt asteroid
• Mazda 121, various models of automobiles produced by Mazda
• Unit 121 - Hezbollah's assassination squad