The aeolian mode is a musical mode or diatonic scale. It was part of the music theory of ancient Greece, and was based around the relative natural scale in A (that is, the same as playing all the 'white notes' of a piano from A to A). This simple scale was called the hypodorian mode in Greek theory, and the aeolian and locrian modes must have been different, perhaps chromatic, variations of this.

The term aeolian mode fell into disuse in mediaeval Europe, as church music was based around eight musical modes: the relative natural scales in D, E, F and G, each with their authentic and plagal counterparts.

In 1547, Heinrich Glarean published his Dodecachordon. Central to its premise was the idea that there were twelve diatonic modes rather than eight. It seems that the additional modes were used in popular folk music, but were not part of the official church repetoire. Galrean added aeolian as the name of the new ninth mode: the relative natural mode in A with the perfect fifth as its dominant, reciting note or tenor. The tenth mode was the plagal version of the aeolian mode, called hypaeolian (under aeolian), based on the same relative scale, but with the minor third as its tenor, and having a melodic range from a perfect fourth below the tonic, to a perfect fifth above it.

As mediaeval monophonic church music was replaced by polyphonic music, the folk modes added by Glarean became the basis of the minor/major division of classical European music: the aeolian mode being the natural minor mode.

The aeolian mode consists of the same components as the major mode with the minor's sixth scale degree as its tonic. Some examples are:

• C Aeolian mode is the E♭ major scale starting on C; the key signature has three flats.
• G Aeolian mode is the B♭ major scale starting on G; the key signature has two flats.
• D Aeolian mode is the F major scale starting on D; the key signature has one flat.
• A Aeolian mode is the C major scale starting on A; the key signature has no sharps or flats.
• E Aeolian mode is the G major scale starting on E; the key signature has one sharp.
• B Aeolian mode is the D major scale starting on B; the key signature has two sharps.
• F# Aeolian mode is the A major scale starting on F#; the key signature has three sharps.
• C# Aeolian mode is the E major scale starting on C#; the key signature has four sharps.

The Aeolian mode's intervallic formula when compared to the major scale consists of flatting the 3rd, 6th, and 7th scale degrees.

Many popular songs, such as the lulaby, Summertime, from the 1935 Porgy and Bess musical, are in the Aeolian mode.