High order radiative corrections in reactions involving electrons and protons

Radiative corrections for elementary processes as elastic electron-proton scattering and electron-positron annihilation into proton-antiproton (and the time reverse reaction) are discussed. The knowledge of hadron characteristics as electromagnetic form factors heavily depends on the radiative corrections applied to the experimental observables and on the assumed reaction mechanism. A compared analysis of scattering and annihilation reactions, on the basis of fundamental symmetries, allows to formulate model independent statements that are a necessary guide for model calculations.