Diapason may refer to:
Diapason (interval), the name of the just octave in Pythagorean tuning Diapason (pipe organ), a tonal grouping of the flue pipes of a pipe organ Diapason (magazine), a French classical music magazine The Diapason (magazine), an American magazine for organ builders and players Diapason normal, the official French standard of concert pitch Diapason, a 1978 novel by Thomas Sullivan Diapason, a mission in the 2006 combat flight simulator Ace Combat Zero: The Belkan War
See also Tuning fork (diapason in Italian and French)