If you write EmacsLisp in your LaTeX documents, you might want to have emacs-lisp-mode active when editing the Lisp, and latex-mode when editing the rest of the file. The solution is to use MultipleModes.
Here is a solution using two-mode-mode, by EdwardOConnor:
(require 'two-mode-mode)
(setq two-mode-rmatch "\\end{elisp"
two-mode-lmatch "\\begin{elisp"
default-mode '(latex-mode "LaTeX")
second-mode '(emacs-lisp-mode "Emacs-Lisp"))
(two-mode-mode)
See LiterateEmacsLisp for a complete example of how to do this.