Observation of the GZK Cutoff by the HiRes Experiment

The High Resolution Fly's Eye (HiRes) Experiment has observed the GZK cutoff. It is seen at $6x10^{19}$ eV, the expected energy for the Greisen Zatsepin Kuz'min threshold. An ``ankle'' structure is seen a decade below the suppression. We present a description of the experiment, data acquisition, analysis and fits to the resulting spectra. The significance of the break in the spectrum is shown to be greater than 5 sigma.