On, on, or ON may refer to:

• Ontario, Canada
• A switching state, contrasted with off (state)
• "being" in ancient Greek
  • Ontology, a branch of philosophy that deals with the concept of being (on)
• ON, the postnomial abbreviation used by members of the Jamaican Order of the Nation
• ON, the postnomial abbreviation for Old Nottinghamian, a person who attended or worked at Nottingham High School
• On, a transliteration of the Egyptian name of the city of Heliopolis
• On, (Genesis 41:45), connected with "Potipherah, priest of On" (where On may refer to Heliopolis or an Egyptian deity)
• ON Semiconductor, a leading supplier of power management solutions
• Old Norse, a North Germanic language commonly referenced in etymology
• Osteonectin, a glycoprotein
• osteonecrosis
• Overground Network, a railway scheme in South London
• Nintendo On, a fake video game console
• Air Nauru, IATA airline designator ON
• ITV Digital, a failed British digital television service originally named ONdigital
• Leg side, in the game of cricket
• The On'yomi reading of Japanese kanji characters

[ In popular music

• ON (album), an album by Gary Glitter
• On (Echobelly album), an album by Echobelly
• On (EP), by Aphex Twin
• On (Imperial Teen album), a 2002 album by Imperial Teen
• ON (music), a musical project by Ken Andrews of Failure

[ See also

• Onji
• Yōon