The key of a piece is its tonal center—the note and chord that feel like home. Music in the key of C major, for example, tends to begin and end on C and uses the notes of the C-major scale as its primary material.

Key signatures at the beginning of a staff show which notes are consistently raised or lowered. Modulation occurs when the music moves to a different key, temporarily or permanently. The relationships between keys form the basis of much tonal composition and analysis.

Listeners sense key even without theoretical knowledge. A piece that ends away from its home key can feel unresolved. Composers choose keys for practical reasons (instrument ranges, vocal comfort) and for expressive color, although the emotional associations of particular keys are partly cultural and historical.

• Tonal center of a piece
• Indicated by key signature
• Can change through modulation
• Organizes melody and harmony