The diffractive dissociation of virtual photons, γ∗ p → Xp, has been studied in ep interactions at HERA with the H1 and ZEUS detectors. The data are presented in terms of the diffractive structure function F2D. The t and the φ dependences of the cross section are measured. A new NLO DGLAP QCD fit is performed to the H1 data. The resulting parton densities are used to predict diffractive dijet and charm cross sections at HERA and the Tevatron, as a test of factorization in hard diffraction.