Niklas Luhmann, a renowned sociologist, developed a productivity system called Zettelkasten, which he used to write over 70 books and nearly 400 academic articles. The system consists of numbered index cards, or slips, filed in six large cabinets, each containing a single idea or concept, known as an "atomicity." Luhmann's method allows for low barrier to entry, and relations between notes are key, with links between notes exponentially increasing the value of the system. He connected his ideas using unique index numbers and explicit reference links, creating a conversational partner that challenged him and prodded him on to greater productivity. Today, the Zettelkasten method has been adapted to fit various workflows and information management systems, including digital applications such as Roam and Obsidian, which offer robust full-text search, non-hierarchical organization, and access to notes from anywhere or any device.