Composition studies of Ultra High Energy Cosmic Rays at the Pierre Auger Observatory

To understand the origin and nature of Ultra High Energy Cosmic Rays their mass composition must be known. The Pierre Auger Observatory is an instrument which provides valuable information for the determination of the primary mass. Different parameters that describe various characteristics of the shower development and at the same time are sensitive to the primary mass are discussed. Their energy dependence and a comparison with predictions from different models are also presented.