Ultra High Energy Cosmic Rays: A Short Review
  We will review the main physical aspects of Ultra High Energy Cosmic Rays. We will discuss in particular their propagation through astrophysical backgrounds, focusing on the latest experimental observations of HiRes, Telescope Array and Auger. We will also review the issue of the transition between galactic and extra-galactic cosmic rays. 
R. Aloisio
astro-ph.HE hep-ph