Abstract: Quantized vortex lines allow a superfluid to rotate, and they are therefore important in superfluid, or quantum, turbulence. Turbulence often involves the flow of energy in a cascade from large scales to small scales. The way in which Kelvin waves on vortex lines can, through non-linear interactions, contribute to this flow will be discussed. Kelvin-wave cascades are likely to play a crucial role in the decay of quantum turbulence in liquid 4He at very low temperatures.