AUCTeX – Emacs support files for TeX

AUCTeX is an extensible package that supports writing and formatting TeX files for most variants of GNU Emacs. In recent versions of XEmacs, AUCTeX is usually already available as a package, though not necessarily up to date. AUCTeX supports many different TeX macro packages, including AMS-TeX, LaTeX, and Texinfo. ConTeXt is not yet supported, volunteers to change this would be welcome.

Note that AUCTeX bundles its own copy of the LaTeX preview package.