  We describe those reproducing kernel Hilbert spaces of holomorphic functions
on domains in ${\Bbb C}^d$ for which an analogue of the Nevanlinna-Pick theorem
holds, in other words when the existence of a (possibly matrix-valued) function
in the unit ball of the multiplier algebra with specified values on a finite
set of points is equivalent to the positvity of a related matrix. Our
description is in terms of a certain localization property of the kernel.
