|Relative key||F? minor|
|Parallel key||A minor|
|Dominant key||E major|
|A, B, C?, D, E, F?, G?|
A major (or the key of A) is a major scale based on A, with the pitches A, B, C?, D, E, F?, and G?. Its key signature has three sharps. Its relative minor is F? minor and its parallel minor is A minor. The key of A major is the only key where a Neapolitan sixth chord on requires both a flat and a natural accidental.
The A major scale is:
In the treble, alto, and bass clefs, the G? in the key signature is placed higher than C?. However, in the tenor clef, it would require a ledger line and so G? is placed lower than C?.
Although not as rare in the symphonic literature as sharper keys, examples of symphonies in A major are not as numerous as for D major or G major. Beethoven's Symphony No. 7, Bruckner's Symphony No. 6 and Mendelssohn's Symphony No. 4 comprise a nearly complete list of symphonies in this key in the Romantic era. Mozart's Clarinet Concerto and Clarinet Quintet are both in A major, and generally Mozart was more likely to use clarinets in A major than in any other key besides E? major. Moreover, the climax part of Tchaikovsky's Violin Concerto is also in A major.
A major occurs frequently in chamber music. Franz Schubert's Trout Quintet and Antonín Dvo?ák's Piano Quintet No. 2 are both in A major. Johannes Brahms, César Franck, and Gabriel Fauré wrote violin sonatas in A major. In connection to Beethoven's Kreutzer Sonata, Peter Cropper said that A major "is the fullest sounding key for the violin."
According to Christian Friedrich Daniel Schubart, A major is a key suitable for "declarations of innocent love, ... hope of seeing one's beloved again when parting; youthful cheerfulness and trust in God."
For orchestral works in A major, the timpani are typically set to A and E a fifth apart, rather than a fourth apart as for most other keys. Hector Berlioz complained about the custom of his day in which timpani tuned to A and E a fifth apart were notated C and G a fourth apart, a custom which survived as late as the music of Franz Berwald.