A yak is a long-haired species of cattle. There are two types of yak:

• Domestic yak (Bos grunniens)
• Wild yak (Bos mutus)

Yak may also refer to:

• Yak (band), an English rock band
• YAK (cryptography) is a public-key authenticated key agreement protocol
• Yak (Thailand), a mythical ogre of the Yasha kind
• Yak (instrument), a type of flute
• "Yak", English game designer Jeff Minter
• "The Yak", Nigerian footballer Yakubu
• Yakovlev or Yak Aircraft Corporation, or numerous aircraft designed or manufactured by this company
• Rheinmetall MAN Military Vehicles YAK, an armoured transport vehicle
• Yak-B 12.7mm machine gun, a Russian .50 caliber four-barrel gatling gun
• Yak Peak, a mountain in British Columbia, Canada
• A member of a yakuza organization
• IATA airport code for Yakutat Airport in Yakutat, Alaska