  A comprehensive theory of nuclear magnetic relaxation is developed for
Haldane Gap materials using nonlinear sigma, boson and fermion models. We
include a thorough discussion of of the effects of interchain couplings,
nearest neighbour hyperfine couplings and crystal structure. We also introduce
a new theory of impurities corresponding to broken chain ends weakly coupled to
bulk magnons. The work is compared to recent experiments on NENP.
