D major (or the key of D) is a major scale based on D, consisting of the pitches D, E, F♯, G, A, B, and C♯. Its key signature consists of two sharps. Its relative minor is B minor and its parallel minor is D minor.

D major is well-suited to violin music because of the structure of the instrument, which is tuned G D A E. The open strings resonate sympathetically with the D string, producing a sound that is especially brilliant. This is also the case with all other orchestral strings.

It is thus no coincidence that many classical composers throughout the centuries have chosen to write violin concertos in D major, including those by Mozart (No. 2, 1775, No. 4, 1775); Ludwig van Beethoven (1806); Paganini (No. 1, 1817); Brahms (1878); Tchaikovsky (1878); Prokofiev (No. 1, 1917); Stravinsky (1931); and Korngold (1945).

It is appropriate for guitar music, with drop D tuning making two Ds available as open strings. For some beginning wind instrument students, however, D major is not a very suitable key, since it transposes to E major on B-flat wind instruments, and beginning methods generally tend to avoid keys with more than three sharps.