  We discuss the perturbative QCD description of diffractive deep-inelastic
scattering, and extract diffractive parton distributions from recent HERA data.
The asymptotic collinear factorisation theorem has important modifications in
the sub-asymptotic HERA regime. In addition to the usual resolved Pomeron
contribution, the direct interaction of the Pomeron must also be accounted for.
The diffractive parton distributions are shown to satisfy an inhomogeneous
evolution equation, analogous to the parton distributions of the photon.
