Niklas Luhmann implemented his Zettelkasten with simple paper index cards (zettels), pens to take notes, and wooden files (kasten). His idea was to take notes on those index cards and store them in a way they could be easily located for further use. He also developed a special numbering system, so zettels had a meanigful, unique identifier. Therefore, it was easier to keep zettels organized, and allowed zettels to be referenced by other zettels. With this ingenious artifact, it was possible to organize and make connections between zettels in different ways.


Note: In terms of knowledge management, Luhmann's system allowed:
  • Record notes of different types on zettels.
  • Identify zettels with unique numbers.
  • Store zettels in the Zettelkasten in an orderly manner.
  • Locate and retrieve zettels from the Zettelkasten using the unique number as a key.
  • Connect zettels to each other by referencing them.
  • Categorize zettels using tags.
  • Create collections of related zettels, also using tags.

Specific characteristics of a Zettelkasten include:

  1. a) It's hypertext-based.
  2. b) The goal is that each zettel contains one and only one idea, concept or unit of knowledge.
  3. c) Emphasis in connecting notes thoughts, not collecting them.
  4. d) Zettelkasten is a personal knowledge tool, not collective.
  5. e) Zettels have a very simple structure:
    • At the top, a unique identifier.
    • In the middle, the body of the zettel with the note.
    • At the bottom of the zettel, references — other zettels, the source of the knowledge you captured, or blank if you captured your own thoughts.
  6. f) Zettels can be freely categorized using tags.
  7. g) Special types of zettels, e.g. hub notes — hub note is a zettel containing only references to other zettels, like an index of interconnected thoughts.

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