SEN is a three-letter abbreviation which may stand for:

• SEN 1116, sports radio station in Melbourne, Australia
• Senator, as a special status with an airline
• Small extension node
• Software Engineering Notes
• London Southend Airport, IATA airport code
• Special Educational Needs
• State Enrolled Nurse
• Sony Entertainment Network

Sen may refer to:

• Etymologically related to the English word cent; a hundredth of the following currencies:
  • Brunei dollar
  • Cambodian riel
  • Malaysian ringgit
  • Indonesian rupiah
• Etymologically unrelated to the English word cent; a hundredth of the following currency:
  • Japanese yen

Sen is a Turkish surname. Notable people with the surname include:

• Ali Sen, Turkish actor
• Eren Sen, German-Turkish footballer
• Gülhan Sen, Turkish television presenter, producer, and speaker
• Sener Sen, Turkish actor
• Volkan Sen, Turkish footballer

A Senate is a deliberative assembly, often the upper house or chamber of a bicameral legislature or parliament. The name comes from the ancient Roman Senate (Latin: Senatus), so-called as an assembly of the senior (Latin: senex meaning "the elder" or "the old one") and therefore allegedly wiser and more experienced members of the society or ruling class.