GY, Gy, or gy may refer to:
Units of measurement Gray (unit) (Gy), SI unit of absorbed radiation Giga-year, 1,000,000,000 years (non-SI) Galactic year, the time it takes for the Solar System to orbit the Galactic Center
Businesses and organisations Gabon Airlines (IATA:GY) GenCorp (NYSE:GY) Green Youth (disambiguation), a Green party youth wing
Language Hungarian gy, an alphabetic digraph gy, a digraph in the Tibetan pinyin transliteration system
People Pierre Gy (1924–2015), French chemist and statistician Garin de Gy, 14th century Catholic Master of the Order of Preachers
Places United Kingdom GY postcode area, of the Bailiwick of Guernsey Great Yarmouth Grimsby
Elsewhere Guyana (ISO 3166: GY) Gy, Haute-Saône, France Gy, Switzerland
Science and technology .gy, the country code top level domain (ccTLD) for Guyana Mazda GY, a car engine Grapevine yellows, a plant disease Gy, the on-line charging interface in the GPRS core network