If you create a piece of software, you need to worry about the users. But if you create an API, then your users are people you’ve never met, who will be using your software on a regular basis — and who will create applications and services based on the API you created. This means that if you  make mistakes when creating the API, you’ll be forced to live with those mistakes, and support them, for some time. How can you create, and then maintain, an API with a minimum of of fuss, and in a way that you can fix mistakes? In this talk, Philipp Meier describes the mistakes that he has made when writing APIs in Clojure. His lessons are appropriate not only for Clojure developers, but for people using other languages, too.