What is the Zettelkasten Research Method?

What is the Zettelkasten Method?

The Zettelkasten method is one of the most effective note-taking methods. But it's not known by many people. The word Zettelkasten means "box of cards" in German. This method was developed by Niklas Luhmann, a German sociologist. He may not be as well known as some scholars such as Richard Feynman, Albert Einstein or Stephen Hawking. But what makes him stand out from the crowd is not just the fact he was an exceptional scholar, but also his writing efficiency. In 30 years, he published 58 books and hundreds of articles.

How did he manage to write so much?

It's thanks to his unique knowledge management system - Zettelkasten.

Zettelkasten allowed him to:

  1. build a huge web of knowledge,
  2. retrieve the right memory when needed,
  3. find meaningful connections among topics, and
  4. develop his ideas, arguments and discussions efficiently.

How to Implement Zettelkasten

The process of Zettelkasten is simple. As the name suggests, it involves boxes and cards.

Luhmann had two boxes: one for bibliographical notes with the references and brief notes about the content of the literature, and the main box where he collected and created new ideas and insights.

  1. Take Literature Notes

The first step of Luhmann's Zettelkasten is taking literature notes as you read something. These notes contain what you don't want to forget or think you might use in your writing or thinking. But, you have to be careful that a) it has to be brief to make it easy to review later, and b) you have to write it in your own words. This means no copy and pasting. Writing in your own words may take a while, but it forces you to really understand what they mean.

  1. Take Bibliographical Notes

The second step is taking bibliographical notes whenever you finish reading something. Luhmann wrote down the reference information on one side of a small index card and a brief note about the content on the other side. Then he keeps the cards in the bibliographical box with the literature notes.

  1. Make Permanent Notes

The third step -- probably the most important step -- is making permanent notes. Go through each note you made in the previous step while thinking about how they relate to what you're learning, your interests, thinking or research. Your goal is not to collect as many notes as possible but to add new values to your existing ideas, arguments and discussions.

What's important here is finding meaningful connections between what you just learned and what you already know. By doing so, you build a web of knowledge. The more web of knowledge you develop, the easier it becomes to learn and retrieve information from your brain. This is because the more information means more hooks we can use to connect the new information to. And the more connected information also means more cues we can use to trigger the right memory.

To find such connections efficiently, ask yourself:

How does this idea fit into what I know?

Can this be explained by something else?

Is this similar to that argument I know? What does X mean for Y?

How can I use this idea to explain something else?

Additionally, it's important to find keywords in your notes to find connections among notes. But finding a keyword is not about where to store a note, but about how to retrieve it. When deciding a keyword, many people ask: which keyword is the most fitting, or which category does this note fall into? Rather, you should ask yourself: In which circumstances will I want to stumble upon this note, even if I forget about it?  

An Example of finding the right keywords, from How to Take Smart Notes by Sönke Ahrens:

"Let's assume I want to add a short note that says: Tversky/Kahneman(1973) showed in an experiment that people are more likely to overestimate the likelihood of an event to happen if they are able to conceive it well and in detail than if it were abstract.

If you think in terms of archiving[where to store], you might feel keywords like 'misjudgement', 'experimental psychology', or 'experiment' would be fitting. In this case, you would think of general categories like 'subject', 'discipline', or 'method'. It is rather unlikely that you will ever think of writing an article based on all notes to 'experimental psychology' or see the need for retrieving all notes filled under 'experiment'.  

Keywords should always be assigned with an eye towards the topics you are working on or interested in, never by looking at the note in isolation."

After finding connections, add your new permanent note to the main box by:

a) filing each one behind relevant notes,

b) adding links to relevant notes, and

c) indexing in the way you can easily discover it later

(One extra step you may need is taking fleeting notes. They are temporary holders of your ideas and thoughts that pop into your mind (e.g. ideas you get while taking a shower or walk). Always keep a pocket notebook or a piece of paper with you so you can write anytime. You should review your fleeting notes within a few days before you forget what you meant. And you can develop them into permanent notes if necessary.)

  1. Find a Topic to Write About

After repeating those steps for a while, you will have developed a huge web of knowledge. Now, whenever you need to find a topic to write about, turn to your box of cards and see lines of cards you developed. See what is missing and what questions arise. You can then read more and take notes to develop your ideas and arguments further.

When you're done with this process, you will already have a wealth of information in your hands. This means you don't have to start from scratch when you write. All you have to do now is reassemble your notes into a logical order and translate them into something coherent.


Writing can be intimidating. You may want to look for fancy writing apps, productivity tips or more stationery. But these things are not necessary. Rather, they can hurt your productivity by increasing the number of decisions you have to make, which reduces your willpower and mental resources. To be more efficient, you have to simplify your workflow. Perhaps, a pen, index cards and slip-boxes are all you need, as shown by Luhmann. Once you have a simple workflow, you need to learn to take smart notes:

  1. Take literature notes (information you don’t want to forget, or think you’ll use later)
  2. Take bibliographical notes so you can reference or come back if needed
  3. Create permanent notes which will be embedded into your web of knowledge
  4. Find meaningful connections among notes, using keywords and questions.

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