  The current status of the ultrahigh energy cosmic ray (UHE CR) enigma and
several proposed solutions involving particle physics beyond the standard model
are discussed. Emphasis is given to top--down models, and as a main example,
supermassive dark matter as galactic source for UHE CR and the status of its
experimental signatures (galactic anisotropy, chemical composition and
clustering) is reviewed. Then different approaches to calculate fragmentation
spectra of supermassive particles are discussed. Finally, it is argued that UHE
neutrinos cannot be - neither directly or indirectly - responsible for the
observed vertical air showers.
