Due to historical confusion, Lydian mode can refer to two very different musical modes or diatonic scales.

Greek Lydian mode

The Lydian mode is named after the ancient kingdom of Lydia in Anatolia. In Greek music theory it was based on the Lydian tetrachord: a series of rising intervals of two whole tones followed by a semitone. Applied to a whole octave, the Lydian mode was built upon two Lydian tetrachords separated by a whole tone. This is identical to the modern major mode: C D E F | G A B C. Placing the two tetrachords together, and the single tone at bottom of the scale produces the Hypolydian mode (below Lydian): F | G A B C | (C) D E F. Placing the two tetrachords together, and the single tone at the top of the scale produces the Hyperlydian mode (above Lydian), which is effectively the same as the Hypophrygian mode: G A B C | (C) D E F | G. Confusingly, the Greek Lydian mode is the same as the mediaeval and modern Ionian mode or major mode.

Mediaeval and modern Lydian mode

The early Christian church developed a system of eight musical modes (the octoechos ), which mediaeval music scholars related to the ancient Greek modes. misinterpreting the Latin texts of Boethius, mediaeval modes were given the wrong Greek names. Thus, in mediaeval and modern music, the Lydian mode may be considered a major scale with the fourth scale degree of the scale is sharpened or raised. Confusingly, the mediaeval and modern Lydian mode is the same as the Greek Hypolydian mode.

A Lydian scale based on the note C consists of the notes C D E F# G A and B. Alternatively, if we start on the note F, the scale consists of the notes F G A B C D E. This scale can be played on the white notes of a piano without the use of any sharps or flats (black keys) only if started on the note F (F G A B C D E).

The theme tunes for The Simpsons and The Jetsons are written using the Lydian scale.