The older introductions to the work of Niklas Luhmann (1927-1998) have a significant shortcoming: they naturally do not take into account the writings from his later years. Luhmann's main sociological work was only published in 1997 in two extensive volumes: The Society of Society. It forms the concluding part of Luhmann's theoretical cathedral and provides a guide to understanding his systems theory. It is precisely the more recent writings that have been integrated into the overall picture by Walter Reese-Schäfer.