2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/7591We address some current theoretical issues around ultra-high energy cosmic rays. We recall that scenarios producing more gamma-rays than cosmic rays up to high redshift can in general only provide a sub-dominant contribution to the ultra-high energy cosmic ray flux. This includes extra-galactic top-down and the Z-burst scenarios. Finally we discuss the influence of large scale cosmic magnetic fields on ultra-high energy cosmic ray propagation which is currently hard to quantify. The views presented here represent the authors perspective.17 latex pages, 5 ps figures included, review given at the 2004 Cracow Epiphany Conference on Astroparticle Physics, to appear in the proccedings in Acta Physica Polonica BAstrophysicsHigh Energy Physics - Phenomenologytext