The Oxford Union, founded in 1823, is a debating society, rather than (as in most universities) a political/welfare organisation (a role played by the Oxford University Student Union).
It also arranges social events and visits by outside speakers. Notable guests have included Mother Teresa, Henry Kissinger, Ronald Reagan and the Dalai Lama.
Being elected to one of the offices of the Union (Secretary, Treasurer, Librarian, President) is traditionally seen as an important stepping stone to a career in politics.
Among those who have served as president of the Union are the British Liberal Prime Minister, Herbert Asquith; the Conservative Prime Minister, Edward Heath; the former Labour politician, Tony Benn; the former Liberal Party leader, Jeremy Thorpe; and Boris Johnson, the Mayor of London.