G1, G01, G.I, G-1, or G One may refer to:

Science and technology

* G1 phase, in the cellular cycle * G1 regulatory sequence for the insulin gene * ATC code G01 ''Gynecological antiinfectives and antiseptics'', a subgroup of the Anatomical Therapeutic Chemical Classification System * Alkali metal, Group 1 of the periodic table * G1, an informal group of fossil bird eggs from the Gobi desert that were later named ''Gobioolithus, Gobioolithus minor''

Astronomy

* Globular cluster Mayall II * YGKOW G1, a giant elliptical galaxy that lensed the Twin Quasar * G1 star, a subclass of stellar classification, G-class stars * G1, a cloud that passed by Sagittarius A* around 2001-2002 * g1, temporary designation of minor planet , a ''New Horizons'' flyby candidate

Computing

* Garbage-first collector, of the Oracle HotSpot Java virtual machine * G1, in ISO 2022 character sets, one of 4 groups of characters that may be swapped into the encoding space via control codes

Cameras

* Contax G1, a Rangefinder camera made by Contax * DSC-G1, a 2007 Sony Cyber-shot G series camera model * PowerShot G1, a Canon camera * Panasonic Lumix DMC-G1, a digital camera made by Panasonic

Military

* Ordnance QF 25 pounder (South African Army designation: G1) * G-1 (submarine), a class of early-20th century submarines constructed by the Lake Torpedo Boat Company of Bridgeport, Connecticut and purchased by the US Navy * Char G1, a French tank * G1, the designation used by the West German and Turkish armies for the FN FAL rifle * G.I, a German designation for several World War I heavy bombers: ** AEG G.I ** Albatros G.I, a German aircraft whose development was the Albatros G.II 1916 aircraft ** Friedrichshafen G.I ** Gotha G.I ** Hansa-Brandenburg G.I, a 1916 bomber aircraft * Fokker G.I, a 1937 Dutch heavy twin-engined fighter plane * G-1 military flight jacket, a type of flight jacket * Kampfgeschwader 55 (historic ''Geschwaderkennung'' code ''G1''), with the Luftwaffe in World War II

Sports

* G1 Climax, an annual professional wrestling singles tournament held by New Japan Pro Wrestling * Group One, the highest level races in horseracing

Transportation

* G1 Aviation G1, French ultralight aircraft * G1 Beijing–Harbin Expressway, in China * Alfa Romeo G1, a 1921 Italian car * Gorkha Airlines (IATA airline designator) * One of the G-series (Toronto subway car), G-series Toronto subway cars

Other uses

* G1 (website), a Brazilian news portal owned by Grupo Globo * G1 Group, a Scottish hospitality and leisure operator * G1 licence, the first tier in the graduated licensing programme for Ontario's new drivers * G.One (character), an android super hero * Gangwon No.1 Broadcasting, a Seoul Broadcasting System television channel in Gangwon Province * T-Mobile G1, the first publicly available Android smartphone * Transformers: Generation 1, a toy line which ran from 1984 to 1992 ** The Transformers (TV series), ''The Transformers'' (TV series), an animated television series meant to promote the toy line (popularly referred to as Generation 1)