降C大调是一个基于C♭音的大调，由C♭、D♭、E♭、F♭、G♭、A♭、B♭和C♭组成，调号有七个降号，即所有的音也有降号。相对小调是降A小调，并行小调是降C小调，与B大调异名同音。

C♭ major is a major scale based on C♭, consisting of the pitches C♭, D♭, E♭, F♭, G♭, A♭, and B♭. Its key signature has seven flats.

C♭ major is the only major or minor key, other than theoretical keys, which has "flat" or "sharp" in its name, but whose tonic note is the enharmonic equivalent of a natural note (a white key on a keyboard instrument).