Ultra-high energy cosmic rays have been detected up to energies of 3 x
1020 eV, and their existence poses several questions. We don't know what they are, how they are accelerated to such energies nor how they manage to propagate up to us if they come from extragalactic sources. I will discuss some aspects of UHE cosmic ray propagation, such as the photodisintegration of nuclei with the cosmic photon background, the possibility of observing their disintegration with solar photons, and the effects of the galactic magnetic field on the extragalactic CR fluxes. This last can lead to important effects, such as a change in the CR spectrum due to magnetic lensing or the appearance of multiple images of CR sources which could be relevant for future detectors such as the Auger Observatory.