Observations of nuclear spin waves in doubly spin polarized atomic hydrogen below 0.6K are discussed. Spin wave spectra have been measured in a field of 8 tesla under various conditions of density, temperature and field gradient by means of both pulsed and cw magnetic resonance at a frequency of 1 GHz. The spectra are understood in terms of identical spin rotational scattering giving rise to a coherent wave, or alternatively, in terms of an approach based on many body theory. Recently observed non linear effects are also discussed. Spin wave phenomena in hydrogen will be compared with spin waves in other fluid systems including liquid 3He, spin polarized 3He gas and atomic deuterium.