A twin is one of two offspring produced in the same pregnancy.

Twin may also refer to:

• Twin, Alabama, a city in the United States
• Twin, Belgium, Walloon name of the Belgium city of Thuin
• Twin (production team), a Swedish record production and songwriting team
• Twin (TV series), a Norwegian television crime drama series from 2019
• Twin (windowing system), a windowing environment for text mode displays
• "Twin (song)", a song by Roddy Ricch featuring Lil Durk
• "Twin", a song from the album Ruby by Jennie
• Twin pattern, software design pattern
• Willows TWIN, a Windows emulator
• Twin, a member of the Minnesota Twins baseball team
• Flat-twin engine
• V-twin engine
• Straight-twin engine, also referred to as a parallel-twin
• Crystal twin, a crystal sample with two domains containing a twin boundary
• Twin house, semi-detached housing
• Twin towns and sister cities, towns and cities involved in town twinning
• Gemini Twin, an American two-seat powered parachute design
• Air Creation Twin, a French two seat ultralight trike design

• Peter J. Twin (born 1937), English nuclear physicist

• Twin paradox, a thought experiment
• Twin prime, a type of prime number
• Twin Range, a mountain range in the U.S. state of New Hampshire
• Twinning (disambiguation)
• Twins (disambiguation)
• The Twin (disambiguation)
• Twin Sisters (disambiguation)
• Gemini (disambiguation)