Music layering means composing a game's soundtrack as separate stems -- drums, bass, melody, pads, strings, percussion -- that play simultaneously but can be independently faded in or out based on gameplay context. Walking through a peaceful village might play just the soft guitar layer. Spot an enemy and the percussion fades in. Enter full combat and every stem is blasting. The music is always the same composition, so transitions feel seamless rather than jarring. This technique requires composers to write music where every possible combination of stems sounds good together, which is a deeply challenging creative constraint.