A source for auto-complete-mode, using etags as a source. Add the following to your emacs setting file such as .emacs: ======================================== (require 'auto-complete-etags) (add-to-list 'ac-sources 'ac-source-etags) ;; If you want this to show documentation, also add the following: (setq ac-etags-use-document t) ======================================== However, for now, it only supports c-mode for showing-documentation purposes. Completing functionality is available possibly in any modes. Of course, you have to visit TAGS file created by etags program. To visit TAGS file, use M-x visit-tags-table. Or if you want to choose another tag file rather than that currently in use, use M-x select-tags-table. Here's part of my settings: ======================================== ;;; function to be called when entering c-mode. (defun my-c-mode-common-hook-func () (interactive) "Function to be called when entering into c-mode." (when (and (require 'auto-complete nil t) (require 'auto-complete-config nil t)) (auto-complete-mode t) (make-local-variable 'ac-sources) (setq ac-auto-start 2) (setq ac-sources '(ac-source-words-in-same-mode-buffers ac-source-dictionary)) (when (require 'auto-complete-etags nil t) (add-to-list 'ac-sources 'ac-source-etags) (setq ac-etags-use-document t)))) (add-hook 'c-mode-common-hook 'my-c-mode-common-hook-func) ========================================