The High Elevation Auger Telescopes (HEAT) are three tiltable fluorescence telescopes which represent a low energy enhancement of the fluorescence telescope system of the southern site of the Pierre Auger Observatory in Argentina. The Pierre Auger Observatory is a hybrid cosmic ray detector consisting of 24 fluorescence telescopes to measure the fluorescence light of extensive air showers complemented by 1600 water Cherenkov detectors to determine the particle densities at ground. In this configuration air showers with a primary energy of 10^18 eV and above are investigated. By lowering the energy threshold by approximately one order of magnitude down to a primary energy of 10^17 eV, HEAT provides the possibility to study the cosmic ray energy spectrum and mass composition in a very interesting energy range, where the transition from galactic to extragalactic cosmic rays is expected to happen. The standard fluorescence telescopes have a field of view (FOV) n elevation up to 30°, HEAT telescopes, instead have a 30°-60° FOV. They worked in combination with the standard Coihueco telescopes.