Propagation of ultra high energy cosmic rays

All particles of energy approaching 1020 eV interact inelastically in the microwave background and other astrophysical photon fields and lose energy. We describe briefly the energy loss processes and show the consequences of proton propagation in extragalactic space. We also discuss the influence of astrophysical magnetic fields on the propagation. To cite this article: T. Stanev, C. R. Physique 5 (2004).