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Measurements of the total cross section for real and virtual photons on protons at center-of-mass energies in the range from 20 GeV to 270 GeV with photon virtualities up to 5000 GeV 2 are presented. For real photons this cross section can be described by Regge-motivated models while for virtual photons perturbative QCD can be applied. The measurements of the two HERA collider experiments ZEUS and H1 open the possibility to investigate the interplay between the two theoretical approaches in the transition region as well as the high-energy behavior of the cross sections. The results of total cross section measurements are discussed in the above context.Contribution to the proceedings of the

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