C-sharp major (or the key of C-sharp) is a major scale based on C♯, consisting of the pitches C♯, D♯, E♯, F♯, G♯, A♯, and B♯. It is enharmonically equivalent to D-flat major. Its key signature has seven sharps. Its relative minor is A-sharp minor (or enharmonically B-flat minor) and its parallel minor is C-sharp minor.

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Quick Facts Relative key, Parallel key ...

C-sharp major

Relative key	A-sharp minor
Parallel key	C-sharp minor
Dominant key	G-sharp major (theoretical) →enharmonic A-flat major
Subdominant	F-sharp major →enharmonic G flat major
Enharmonic	D-flat major
Component pitches
C♯, D♯, E♯, F♯, G♯, A♯, B♯

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The C-sharp major scale is:

A harp tuned to C-sharp major has all its pedals in the bottom position. Because all the strings are then pinched and shortened, this is the least resonant key for the instrument.

• Tonic - C-sharp major
• Supertonic - D-sharp minor
• Mediant - E-sharp minor
• Subdominant - F-sharp major
• Dominant - G-sharp major
• Submediant - A-sharp minor
• Leading-tone - B-sharp diminished

Most composers prefer to use the enharmonic equivalent D-flat major since it contains five flats as opposed to C-sharp major's seven sharps. However, Johann Sebastian Bach chose C-sharp major for Prelude and Fugue No. 3 in both books of The Well-Tempered Clavier. In Hungarian Rhapsody No. 6, Franz Liszt takes the unusual step of changing the key from D-flat major to C-sharp major near the start of the piece, and then back again to B-flat minor. Maurice Ravel selected C-sharp major as the tonic key of "Ondine" from his piano suite Gaspard de la nuit. Erich Wolfgang Korngold composed his Piano Concerto for the Left Hand, Op. 17, in C-sharp.

The Allegro de concierto by Spanish composer Enrique Granados is written in C-sharp major. Canadian composer and pianist Frank Mills originally wrote and performed his instrumental hit "Music Box Dancer" in C-sharp major; however, most modern piano editions have the piece written in C major.

Louis Vierne used C-sharp major for the "Dona nobis pacem" of the Agnus Dei of his Messe solennelle in C-sharp minor.

• Lester, Joel (Spring 1978). "The Recognition of Major and Minor Keys in German Theory: 1680–1730". Journal of Music Theory. 22 (1). Duke University Press: 65–103. doi:10.2307/843628. JSTOR 843628.

• List of compositions in C-sharp major