  We review QCD based descriptions of diffractive deep inelastic scattering
emphasising the role of models with parton saturation. These models provide
natural explanation of such experimentally observed facts as the constant ratio
of the diffractive and total cross sections as a function of the Bjorken
variable, and Regge factorization of diffractive parton distributions. The
Ingelman-Schlein model and the soft color interaction model are also presented.
