On, on, or ON may refer to:

• On (band), a solo project of Ken Andrews
• On (EP), a 1993 EP by Aphex Twin
• On (Echobelly album), 1995
• On (Gary Glitter album), 2001
• On (Imperial Teen album), 2002
• On (Elisa album), 2006
• On (Jean album), 2006
• On (Boom Boom Satellites album), 2006
• On (Tau album), 2017
• "On" (song), a 2020 song by BTS
• "On", a song by Bloc Party from the 2006 album A Weekend in the City
• "On", a song by Anson Lo, 2023

• Ön, a 1966 Swedish film
• On (Japanese prosody), the counting of sound units in Japanese poetry
• On (novel), by Adam Roberts
• ONdigital, a failed British digital television service, later called ITV Digital
• Overmyer Network, a former US television network

• On (Ancient Egypt), a Hebrew form of the ancient Egyptian name of Heliopolis
• On, Wallonia, a district of the municipality of Marche-en-Famenne
• Ahn, Luxembourg, known in Luxembourgish as On
• Ontario, a Canadian province

• Operative note, documentation of care relating to an operation
• Optic neuritis, especially relevant in multiple sclerosisA
• Osteonecrosis, death of bone tissue
• POsteonectin, a glycoprotein

• ON Semiconductor, a semiconductor manufacturing company
• O'Nan group, a mathematical group
• OS/Net, the OpenSolaris Community
• On, the proper class of all ordinal numbers

• On, Egyptian name of Heliopolis
• On (biblical figure), son of Peleth
• On (company), a Swiss athletic shoe and sportswear company
• On Kawara, Japanese artist
• Nauru Airlines (IATA airline designator ON)

Ollio

• Old Norse, a North Germanic language commonly referenced in etymology
• Ontology, a branch of philosophy that deals with the concept of being
• On'yomi, reading of Japanese kanji characters
• Order of the Nation, a Jamaican honour
• Overground Network, a railway scheme in South London
• ON convoys, a series of WWII trade convoys
• Orka náttúrunnar (ON Power), Icelandic geothermal power company
• On, a Basque-language honorific equivalent to Spanish Don (honorific)
• On, a preposition

• O(n)
• Yōon