AUCTeX is an extensible package for writing and formatting TeX files in GNU Emacs and XEmacs. It supports many different TEX macro packages, including AMS-TEX, LaTeX, Texinfo, ConTEXt, and docTeX (dtx files).
AUCTeX includes preview-latex which makes LaTeX a tightly integrated component of your editing workflow by visualizing selected source chunks (such as single formulas or graphics) directly as images in the source buffer.
(add-to-list 'load-path "~/.emacs.d/auctex")
(load "auctex.el" nil t t)
(load "preview-latex.el" nil t t)
Configure view program
'((output-dvi "DVI Viewer")
(output-pdf "PDF Viewer")
(output-html "HTML Viewer")))
;; this example is good for OS X only
'(("DVI Viewer" "open %o")
("PDF Viewer" "open %o")
("HTML Viewer" "open %o")))