GI or gi may stand for:

• Gastrointestinal, a division of the human anatomy in medicine.
• "GI" means, in common American usage: "government-issued", "army enlisted personnel".
• G.I. Joe. A toy soldier seriers manufactured by Hasbro.
• Gi is a two-letter English word for a the clothing used in judo, karate and other Japanese martial arts. It is however not correct Japanese; that would be keikogi or dogi.
• Gibraltar's ISO country code.
• Gilbert (Gb or Gi), a former unit of magnetomotive force or magnetic potential.
• Gill (gi), a U.S. customary unit equal to 4 U.S. fluid ounces (never used) and an Imperial unit equal to 5 imperial fluid ounces (rarely used)
• Global illumination; In 3D computer graphics, GI is the rendering of light in 3D scenes.
• The glycemic index is a ranking system for carbohydrates based on their effect on blood glucose levels.
• Gi is also the name of a character in the television series Captain Planet and the Planeteers. See Gi (Captain Planet character).
• GI can refer to "Galvanized Iron".