Diffractive DIS has been established at HERA and detailed information has been extracted on the structure function of the Pomeron mediating the diffractive process. The gluon contribution dominates, about 75 &percent; of the Pomeron momentum is carried by gluons. The experimental results on dijet andD*‐meson production in diffractive DIS are compatible with LO QCD predictions supporting the idea of QCD factorization to be valid.t,Q2andMV2of heavy vector mesons provide a hard scale for the processep→eV p. The measured helicity spin matrix elements for the reactionep→e&rgr;0pare in good agreement with perturbative QCD predictions based on 2‐gluon‐exchange. © 2003 American Institute of Physics