Zettelkasten

Disclaimer: the Zettelkasten method has been recently hijacked by the productivity bros community, but this ancient method of organising data is actually truly useful, even for those whose brain has not be addled by an excess of testosterone.

What is a Zettelkasten?

Zettelkasten is a method of organising information. The name Zettelkasten literally means note-box. In this method information is organised in paper slips similar to index cards. These slips are then kept in boxes and hence the name. Zettelkasten has a great advantage over traditional note keeping (in notebooks, for example): which is allowing a greater degree flexibility when ordering the notes. In a notebook the position of the notes is fixed, while in a Zettelkasten the cards (and hence the notes) can be reshuffled at will. In addition, the Zettelkasten includes links between the notes, as will be explained in more detail below.

The Zettelkasten method evolved over time and, as such, there is not a single method but a large number of similar methods adapted to the individual user’s needs. The history of the Zettelkasten goes back to at least the 16th century (more details here). In modern days, Zettelkasten has evolve to use software instead of note cards. There are many examples of software developed using the ideas behind Zettelkasten. The main one being the web itself, which uses hypertext, ie. webpages connected by links, as one of its key principles. Another one is Wiki, the software used to run Wikipedia and many similar web domains. There are also a large amount of note taking applications for personal or professional use that include this method.

What then defines a Zettelkasten?

What makes a Zettelkasten system particularly useful are the two following properties: (1) a collection of short notes that (2) include links to each other.

In practice this means that notes have the following general format:

1. Notes have 3 sections: top, body, bottom.
2. At the top, the note includes a unique identifier (which will later be used to link other notes to this note) and a title. In addition, tags or other metadata can be included.
3. The body includes the main content of the note. This content will include useful links to other notes using their respective identifier, as mentioned above.
4. the bottom is used to include source (or literary) references. This can be books, webpages, newspaper or other publication articles, etc. It can be left empty if no source was used to write the note.

What are other important “rules” of a Zettelkasten?

A suitable system for generating note identifiers is crucial. There are two reasons for this. The first is that every note must absolutely have a unique identifier for obvious reasons. The other is that, once a note has an identifier, this cannot be easily changed. Changing one of these identifiers will require going through every note and replacing the new identifier in every link to the corresponding note.

An absolute rule when using Zettelkasten is that links should never be used on their own, they must always come after a brief description of their respective content, enough information to make it clear how this content is relevant in the current context. This is essential for clarity purposes and without it the system becomes cumbersome to use.

When using actual cards, the notes are necessarily extremely brief. Paradoxically, it is the brevity of the notes that makes the Zettelkasten method so powerful. Thus, even if using other methods which allow for longer notes, namely software, it is usually ideal to keep notes as brief as possible. Basically, each note should contain a single idea. These ideas are then connected to other ideas forming a coherent set. However, Zettelkasten allows for the extra flexibility that a note can be part of more than one such sets and, in addition, within each set, ideas can be reshuffled and reorganised at will.

The aforementioned sets can be included in the Zettelkasten method by organising them in special notes. These notes do not contain single ideas, like ordinary notes, but instead contain organised lists of links to notes. Note, that these lists must also contain the title (or a brief description of the content) of the respective note. This is essential for clarity as aforementioned.

What do you need before starting a Zettelkasten?

1. Decide the format of your Zettelkasten (note: if you use a proprietary software the following items will be taken care of).
2. Decide what method you will use to generate note identifiers.
3. Decide what notation you will use for links.
4. Decide what format you will use for source references.
5. (Optional) decide what software to use to keep your notes available and synchronised on all your devices.
6. (Optional) decide what method to use to search your notes.

All the above items are developed in more detail in the next sections.

(1) What format to choose?

A physical Zettelkasten requires a set of index cards and a box (or several) to keep them. In comparison, a digital Zettelkasten is considerably easier to keep and will, in addition, have the advantage of being easily transported (you can keep your entire Zettelkasten synchronised over all your digital devices). However, there is mounting evidence that the physical act of writing and handling physical objects, like the cards, helps increasing clarity of thought and creativity (something to keep in mind). In principle, you can keep both a physical Zettelkasten and a digital one. However, this entails extra time and effort copying your notes from one format to the other.

A digital Zettelkasten can be made of simple text files (use a basic text editor software to keep them) or can use a proprietary format (there are many companies providing note taking software). The latter have the advantage that everything is ready-made, you only need to learn to use the software and to adapt it to your needs. The former however have the great advantage that you do not risk losing all your notes if the company stops providing the software. Note that, in order to keep their clients, these companies often use formats that make it very difficult to migrate your notes to other systems. At the speed software evolves, the risk of losing data, when the software becomes obsolete, is a lot larger than most people imagine.

Proprietary softwares use their own system and are ready to use. You will need to learn to use them using their manual or tutorials available online. There is nothing more to say about these. In what follows, I will provide some ideas on out to develop a personal Zettelkasten system.

The text file format is highly recommended for the extra security and flexibility it provides, but it is obviously more difficult to set up.

(2) How to generate identifiers?

There are many method to do this. Note that identifiers are just that, they do not need to be descriptive in anyway. On the contrary, it is easier to keep a system in which they are simple numbers or a combination of numbers and letters. What you need is a method that will make it as simple as possible to make sure you will never make the mistake of using the same identifier for two different notes and, in addition, is flexible enough to include as many notes as you may need during an entire lifetime of note taking.

Here I will mention a few simple ones:

1. use a simple numerical method: for example, label your notes using integer numbers: 1, 2, 3, … If you want to add a note between note 1 and 2, expand it by adding more numbers: 1.1, 1.2, … and add even more layers as needed: 1.1.1, 1.1.1.1, … Remember: as long as the identifier is unique, it can be anything (it does not need to have a fixed length or be meaningful). Numbers, which are naturally ordered, make it easy to keep track of what identifiers have already been used. This system is particularly useful to use in a physical Zettelkasten, where the notes will be placed in a specific order in their archive boxes.
2. use a combination of letters and numbers, similar to the above, but, for example, using: 1, 1.a, 1.a.1, etc (letters have the disadvantage that they are limited).
3. use the date and time of creation of a note: for example, a note created at 18:38 on 29 July 2025 can have the identifier 202507291838. This method is particularly useful for digital Zettelkasten.

I am sure that with a little imagination you can create your own method.

(3) What notation to use for links?

Here again there are many possibilities. Wiki uses double brackets like this: A list of dog breeds can be found in [[1.1.a]].

(4) What notation to use for source references?

I recommend using a standard method. BibTex, for example, is a system that is very popular and easily available (Wikipedia, for example, provides BibTex data for its articles, see Tools -> ‘Cite this page’ on each article.)

(5) Do you want to keep your notes synchronised across devices?

If you use a text editor to create your Zettelkasten, using a proprietary system like Dropbox is probably the best way to keep them backed up and synchronised across devices.

(6) Do you want to be able to search you notes?

Needless to say, that the ability to search through all the note in your Zettelkasten is really useful. This is the only thing you cannot do in a physical Zettelkasten and, thus, the only true advantage of a digital one. It is easy and possible to search your notes in a computer, adding a new level of flexibility to your Zettelkasten. The software to search through text files depends on your operating system, but all modern operating systems include it.

Conclusion

Once you made all these decisions and checked the best way to implement them in practice, you are ready to go. Start taking notes and, of course, migrate your already existent notes to your new system.

References

Wikipedia article
A more detailed introduction