Ultrahigh energy cosmic rays: experimental progress and the puzzles the data present

I will survey the field of ultrahigh energy cosmic rays (UHECRs), report on recent observational developments, and describe the theoretical puzzles presented by the data.  UHECRs are the highest energy particles in nature -- some having more than 10⁸ times higher energy than achieved in an LHC beam.  Learning how nature produces them should reveal some fascinating astrophysics, and exploiting them for particle physics can provide a glimpse of particle interactions at energies beyond the reach of accelerators.