The original Mission: Impossible theme is known for using a 5/4 time signature.
Composer Lalo Schifrin wrote the theme for the 1966 television series, using an unusual five-beat meter that immediately made the music feel tense, off-balance, and distinctive. Most popular themes of the period used more familiar meters, so the rhythm became part of the show’s identity rather than merely background music.
The theme’s five-beat pulse is often associated with the Morse-code pattern for “M.I.”: two dashes followed by two dots. That connection has been suggested as an inspiration, although it cannot be confirmed as Schifrin’s conscious starting point for this particular composition.
Schifrin reportedly wrote the main theme in about 90 seconds. Its visual title sequence cuts images to the music, while the burning fuse became one of television’s most recognizable opening devices. The score’s unusual rhythm is why 4/4, despite being far more common, is not the correct choice.