Since every new scientific work starts with a comprehensive literature study about the state of the art, this paper should give an overview about previous, but still useful, and more recent publications to describe a secondary air system (SAS) for gas turbines. Nevertheless, in current times it is impossible to present a complete research, but the well-disposed reader will get a meaningful insight and may use the references as a start for their own detailed search. The first part will give a description of a typical set up of a SAS and the common flow elements that can be found along the flow path. It also includes an explanation of the elements operating behavior, especially regarding the pressure and temperature changes as well as the resulting air mass flow. In the second part the authors describe the plans at the German Aerospace Centers (DLR) Institute of Test and Simulation for Gas Turbines in the SAS’ field of research.