Turbulence in superfluid helium is unusual and presents a challenge
to fluid dynamicists because it consists of two coupled, inter
penetrating turbulent fluids: the first is inviscid with quantized
vorticity, the second is viscous with continuous vorticity. Despite
this double nature, the observed spectra of the superfluid turbulent
velocity at sufficiently large length scales are similar to those
of ordinary turbulence. I present experimental, numerical and
theoretical results which explain these similarities, and illustrate
the limits of our present understanding of superfluid turbulence.