Nucleon form factors '99

The authors review recent progress in the experimental knowledge of and theoretical speculations about nucleon form factors, with special emphasis on the large Q2 region. There is now a long history of continuous progress in the understanding of electromagnetic form factors at large momentum transfer. After the pioneering works leading to the celebrated quark counting rules, the understanding of hard scattering exclusive processes has been solidly founded. A perturbative QCD subprocess is factorized from a wave function-like distribution amplitude varphi(xi,Q2) (xi being the light cone fractions of momentum carried by valence quarks), the Q2 dependence of which is analyzed in the renormalization group approach. Although an asymptotic expression emerges from this analysis for the x dependence of the distribution, it was quickly understood that the evolution to the asymptotic Q2 is very slow and that indeed some non perturbative input is required to get reliable estimates of this distribution amplitude at measurable Q2