The Zettelkasten method (German: "slip box") is a note-taking system developed by sociologist Niklas Luhmann.

He produced 90,000 index cards and 70 books. The cards are not organized by topic — they're organized by connection.

The key rule: **one idea per note**. A note that contains two ideas should be two notes.

See: [[atomic-notes]], [[@alice/how-i-take-notes]]