  The High Resolution Fly's Eye (HiRes) experiment has observed the GZK cutoff.
HiRes' measurement of the flux of cosmic rays shows a sharp suppression at an
energy of 6 x 10^{19} eV, exactly the expected cutoff energy. We observe the
``ankle'' of the cosmic ray spectrum as well, at an energy of 4 x 10^{18} eV.
We describe the experiment, data collection, analysis, and estimate the
systematic uncertainties. The results are presented and the calculation of a
five standard deviation observation of the GZK cutoff is described.
