The origin of the highest energy cosmic rays has remained a profoundmystery for decades. Physicists are generally interested in cosmic ray sources as potential “beam generators”, providing a source of particles (including, perhaps, neutrinos) with energies far beyond that which could ever be achieved by particle accelerators on Earth. But arguably even more compelling is the underlying astrophysical mystery as to the nature of the accelerating engines for cosmic rays. Are ultra-high energy cosmic rays accelerated in jets of accreting black holes? Do they derive from relativistic shocks in intergalactic space? Are cosmic rays generated during gamma-rays burst events? Or do cosmic rays result from the decay of semi-stable super-massive particles left over from the Big Bang? In this talk, I will look at how the data from cosmic ray experiments can be used to address these questions. I will emphasize in particular new first results from the Pierre Auger Cosmic Ray Observatory, including the spectrum, searches for anisotropy, and constraints on gamma-rays fraction, which already place important constraints on many models for cosmic ray origin.