Unlike all other introductions to system theory, the author himself introduces his theory here. The lecture on system theory that underlies this book showcases Niklas Luhmann at the peak of his mastery over a complex theory and the society it describes. The introduction lives up to its name in that Luhmann aimed to enable his student audience to engage with this theory independently. It is therefore a treasure trove of simple ideas for tackling difficult questions and offers a range of concepts and theorems that allow for the training of perception, description, and thinking—both for observing politics and economics, religion and science, art and education, family and organization, as well as for assessing current issues of cognition.