C# major is a major scale based on C#, consisting of the pitches C#, D#, E#, F#, G#, A#, B# (enharmonic to C natural) and C#. Its key signature consists of seven sharps.
Its relative minor is A-sharp minor. Its enharmonic equivalent is D-flat major.
A harp tuned to C-sharp major has all its pedals in the bottom position.
Although most composers prefer to use the enharmonic equivalent D-flat major because it has just five flats as opposed to the seven sharps of C-sharp major, Johann Sebastian Bach actually chose C-sharp major for Prelude and Fugue No. 3 in both books of the Well-Tempered Clavier.