We present the data on diffractive scattering in electron--proton reactions at HERA and review the analysis of these data in terms of diffractive parton distribution functions. From these a clear picture of the partonic structure of diffractive exchange emerges. The basis of the analysis is the factorization property of diffractive exchange, which is subjected to experimental tests using deep-inelastic diffractive charm and jet production, as well as photoproduction of jets.

PACS numbers: 12.38.Aw, 12.38.Bx, 12.39.St