AUCTeX is a comprehensive customizable integrated environment for writing input files for TeX/LaTeX/ConTeXt/Texinfo using GNU Emacs. Currently XEmacs ships with its own AUCTeX version.

It supports processing source files by running TeX and related tools (such as output filters, post processors for generating indices and bibliographies, and viewers) from inside Emacs. AUCTeX allows browsing through the errors reported by TeX, while it moves the cursor directly to the reported error, and displays some documentation for that particular error. This will even work when the document is spread over several files.

AUCTeX can automatically indent LaTeX source, either line by line or for an entire document, and has a special outline feature which can greatly assist in getting an overview of a document.

AUCTeX is written entirely in Emacs Lisp, and may therefore be enhanced with new features for specific needs. It comes with a large range of handy Emacs macros. It is a GNU project, and documentation for all its features is accessible via the Emacs info browser.