The slip-box, or Zettelkasten, is a revolutionary note-taking system that was the cornerstone of Niklas Luhmann's extraordinary productivity. By writing each idea on a separate index card and linking related notes, Luhmann created a dynamic and flexible network of knowledge. This method enabled him to produce 58 books and hundreds of articles. Ahrens notes, 'Luhmann was able to focus on the important things right in front of him, pick up quickly where he left off and stay in control of the process because the structure of his work allowed him to do this.'