  We review a new theory of orthogonal separation of variables on
pseudo-Riemannian spaces of constant zero curvature via concircular tensors and
warped products. We then apply this theory to three-dimensional Minkowski
space, obtaining an invariant classification of the forty-five orthogonal
separable webs modulo the action of the isometry group. The eighty-eight
inequivalent coordinate charts adapted to the webs are also determined and
listed. We find a number of separable webs which do not appear in previous
works in the literature. Further, the method used seems to be more efficient
and concise than those employed in earlier works.
