  We formulate a prescription for computing Minkowski-space correlators from
AdS/CFT correspondence. This prescription is shown to give the correct retarded
propagators at zero temperature in four dimensions, as well as at finite
temperature in the two-dimensional conformal field theory dual to the BTZ black
hole. Using the prescription, we calculate the Chern-Simons diffusion constant
of the finite-temperature N=4 supersymmetric Yang-Mills theory in the strong
coupling limit. We explain why the quasinormal frequencies of the
asymptotically AdS background correspond to the poles of the retarded Green's
function of the boundary conformal field theory.
