Open questions and perspectives for hadron electromagnetic form factors in space-like and time-like regions

An overview of recent data on electromagnetic hadron form factors is presented and discussed in terms of selected nucleon models in space-like and time-like regions. Model independent properties connecting scattering and annihilation channels are presented and give a deeper understanding of the underlying physics. Radiative corrections are discussed. The interest of polarization observables with respect to model predictions and reaction mechanism (one photon versus two photon exchange) is highlighted.