This post is a part of The Zettelkasten Manual.


Zettelkasten is a non-linear note-filing system originated by Niklas Luhmann, which he referred to as his “second brain.” or so-called a communication partner.

The term “Zettelkasten” is German for “slip box,” referring to the collection of hand-written notes stored in a box and interconnected through references, similar to the hyperlinking of the World Wide Web1 but happened on paper instead of the Internet back to the 1950s.

While similar in form to a personal wiki, the two systems differ in their creation and capabilities. A Zettelkasten can be implemented using a wiki, but not all wikis are Zettelkasten, most of them are not.

Niklas Luhmann

Niklas Luhmann was a professor of Sociology at Bielefeld University for 25 years (1968-1993) and published over 500 articles and books on a wide range of topics. He attributed his unprecedented productivity to his Zettelkasten system, saying in an interview:

I don’t think everything on my own, mostly happens in the slip box.

My productivity can essentially be explained from the slip box system.

The slip box costs me more time than writing a book.

Luhmann’s Slip Box

Luhmann kept notes on small slips of paper stored in a wooden box, resulting in two collections of 90,000 hand-written cards in A6 format, numbered consecutively.

Zettelkasten Photo of “Zettelkasten” from “Niklas Luhmann-Archiv” is licensed under CC-BY-NC-SA 4.0.

The notes consisted of his thoughts, arguments, and concepts, and were not just excerpts, below are some facts about them2 3 4.

  • Two collections in total

  • 90,000 handwritten cards in A6 format

  • Cards are numbered consecutively

  • The notes are not simply excerpts, it consists of his thoughts, theoretical arguments, and concepts

  • The first collection was created when he is a legal expert with interests in constitutional law and administrative sciences to a systems theoretical sociologist

  • Just before(1960 - 1961) he created the second collection, he spent a year at the Harvard School of Public Administration in Cambridge, MA(USA), where he attended lectures by Talcott Parsons, the leading sociologist in the field of systems theory at the time

  • There were no documents in the literary estate substantiating the claim that his visit to Harvard was the trigger to start a new collection of notes, but it seems obvious

First Collection Second Collection
Created 1951 - 1962 1963 - 1997
Handwritten Cards 23,000 67,000
Content His readings in political science, administrative studies, organization theory, philosophy, and sociology sociology
# of Top-level Sections 108 11
Top-level sections state, equality, planning, power, constitution, revolution, hierarchy, science, role, concept of world, information, etc organizational theory, functionalism, decision theory, office, formal/informal order, sovereignty/state, individual concepts/individual problems, economy, ad hoc notes, archaic societies, advanced civilizations
# of Subsections 100
Section Separator a comma: , a slash /
Bibliographies. two, containing 2,000 titles one, incomplete, containing 15,000 references
Keyword Index 1,250 entries 3,200 entries
# of References 20,000 30,000
Average References nearly every card has a ref nearly every second card has a ref

  1. Berners-Lee, Tim. The Original Proposal of the WWW, HTMLized. Mar. 1989,

  2. Schmidt, Johannes F. K. “Der Nachlass Niklas Luhmanns – eine erste Sichtung: Zettelkasten und Manuskripte.” Soziale Systeme, vol. 19, no. 1, Jan. 2014. (Crossref), doi:10.1515/sosys-2014-0111.

  3. Luhmann, Niklas. Bibliographie 1. Universitätsbibliothek Bielefeld, 1 June 2017, Card Index Box.

  4. Luhmann, Niklas. Bibliographie 2. Universitätsbibliothek Bielefeld, 1 June 2017, Card Index Box.