Theme: Theory of Society; Duration: 30 years; Cost: none - this was the famous answer that Niklas Luhmann gave at the end of the 1960s to the question about his research project. The timeline was adhered to: in 1997, "The Society of Society" was published, Luhmann's opus magnum and the centerpiece of this endeavor. As significant as this work is, its backstory is equally remarkable. For as the scientific legacy of the sociologist shows, Luhmann wrote several largely publishable and substantively independent versions of his theory of society over the decades. In 1975, he completed the first of these versions, spanning nearly a thousand typescript pages. It is undoubtedly the most sociologically rich version of a comprehensive theory of society that has emerged from Luhmann's unique research project, and is now published under the title "Sys.".