Polytonality is a musical technique where two or more different keys are used simultaneously in a composition. This creates a rich and complex sound, as each key contributes its own unique tonal qualities. Composers like Igor Stravinsky and Charles Ives often employed polytonality to add depth and texture to their music, challenging traditional harmonic structures. In polytonal music, different instruments or voices may play in separate keys, leading to interesting clashes and harmonies. This approach allows for greater creative expression and can evoke a wide range of emotions, making it a fascinating aspect of modern music composition.