Also written as C# major (same key, different spelling).
5 flats: Bb, Eb, Ab, Db, Gb.
The chords that occur naturally within this key, built by stacking thirds on each scale degree. Tap any of them for the full chord page.
The relative minor of Db major is Bb minor, sharing the exact same key signature. See the chord progressions page for how these chords commonly string together, and the circle of fifths for how every key relates to its neighbors.