To or to may refer to:

• a grammatical particle used in forming the English verbal infinitive
• .to, the Internet domain country code for Tonga
• To, Burkina Faso, one of the 7 departments of the Sissili Province of Burkina Faso
• Johnnie To, Hong Kong film director and producer
• Nihonto - Japanese word for "sword".
• Teraoctet, a unit of information or computer storage

TO may stand for:

• Toronto, "T" stands for Toronto, and "O" stands for Ontario, the province to which Toronto serves as its capital city.
• Toulouse Olympique, a French rugby league club.
• Thousand Oaks, California
• Tonga, ISO 3166-1 alpha-2 country code
• President Airlines, IATA airline designator
• Takeoff
• Telephone operator
• Internet Relay Chat slang for takeover
• A medieval T and O map (orbis terrae)
• Territorial Defense Forces (TO), part of the armed forces of the former SFR Yugoslavia
• In sports:
  • Turnover (disambiguation)
  • Time-out (sport)
  • Terrell Owens, NFL wide receiver
• JEDEC transistor outline
• Talk.Origins, a Usenet discussion forum
• Tactics Ogre, a Japanese tactical role-playing video game series
• Tantra Online, an online computer game
• The Outsiders (novel), a novel by S.E. Hinton
• Thermal oxidizer
• Terrell Owens