The charm contribution Fcc2 to the proton structure function F2 has been measured by the two experiments ZEUS and H1 at the electron-proton collider HERA, in a wide x and Q2 range. Charm has been tagged by different techniques: by the reconstruction of particular charmed mesons in the final state, D*, D0 D+, Ds, or by the inclusive measurement of the displacement of the charm decay products with respect to the event vertex. The data are compared with next-to-leading order QCD predictions.