Studies of the Cosmic Ray Composition with the Pierre Auger Observatory

In the talk we will discuss the the cosmic ray composition of extra galactic cosmic rays and describe the close connection of air shower observables and ultra high energy hadronic interactions. After a short introduction to the Pierre Auger Observatory the study of the composition of ultra high energy cosmic rays with energies above 10¹⁸ eV using the fluorescence telescopes of the observatory will be presented.