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

Greek Dorian mode

The Dorian mode is named after the Dorian Greeks. In Greek music theory it was based on the Dorian tetrachord: a series of rising intervals of a semitone followed by two whole tones. Applied to a whole octave, the Dorian mode was built upon two Dorian tetrachords separated by a whole tone. This is the same as playing all the white notes of a piano from E to E: E F G A | B C D E. Placing the two tetrachords together, and the single tone at bottom of the scale produces the Hypodorian mode (below Dorian): A | B C D E | (E) F G A. Placing the two tetrachords together, and the single tone at the top of the scale produces the Hyperdorian mode (above Dorian), which is effectively the same as the Mixolydian mode: B C D E | (E) F G A | B. Confusingly, the Dorian mode is the same as the mediaeval and modern Phrygian mode.

Mediaeval and modern Dorian 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 Dorian mode is a diatonic scale or musical mode which corresponds to the white keys of the piano, from "D" to "D". It may be considered a major scale which begins on the pitch a whole tone above the major scale's tonic, ie a major scale starting from its second scale degree. Examples include:

• The D Dorian mode contains all notes the same as the C major scale
• The G Dorian mode contains all notes the same as the F major scale
• The A Dorian mode contains all notes the same as the G major scale

The Dorian mode is symmetric, meaning that the pattern of tones and semitones (T-s-T-T-T-s-T) is the same ascending or descending. Examples of the mode's use include "What shall we do with the drunken sailor" and "Scarborough fair".

The Dorian mode is equivalent to the natural minor scale (or the Aeolian mode) but with the sixth degree raised a semi-tone. Confusingly, the Dorian mode is the same as the Greek Phrygian mode.