  A large collection of results for the diffractive dissociation of virtual
photons, $\gamma^{\star}p \to Xp$, have been obtained with the H1 and ZEUS
detectors at HERA. Different experimental techniques have been used, by
requiring a large rapidity gap between $X$ and the outgoing proton, by
analysing the mass distribution, $M_X$, of the hadronic final state, as well as
by directly tagging the proton. A reasonable compatibility between those
techniques and between H1 and ZEUS results have been observed. Some common
fundamental features in the measurements are also present in all data sets.
Diffractive PDFs can give a good account of those features. Ideas and new
developments are discussed in these proceedings.
