Emacs-lisp

Emacs Lisp is a dialect of the Lisp programming language used in the GNU Emacs and XEmacs editors. Emacs Lisp is sometimes called Elisp, which risks leading to confusion with another Lisp dialect of the same name.

Most of Emacs' editing functions come from code written in Lisp; the rest is written in C. Users who want to customize or extend the functionality of Emacs can write code in Emacs Lisp.

Emacs Lisp is related to the Lisp dialects: MacLisp and Common Lisp. It allows imperative and functional programming methods. Lisp was chosen as the extension language for Emacs because of its powerful features, including the ability to treat functions as data.

Writing Emacs Lisp is not the only method of customizing GNU Emacs. Since version 20, GNU Emacs has included the ability to customize common variables through a graphical interface. "Customize" it works when the user writes Emacs Lisp code, and is limited to simple customizations. Not all users need the wide degree of extensibility that Emacs offers. Those who do can write their own Emacs Lisp code.