inf-ruby provides a REPL buffer connected to a Ruby subprocess. If you're installing manually, you'll need to: * drop the file somewhere on your load path (perhaps ~/.emacs.d) * Add the following lines to your .emacs file: (autoload 'inf-ruby "inf-ruby" "Run an inferior Ruby process" t) (add-hook 'ruby-mode-hook 'inf-ruby-minor-mode) Or, for enh-ruby-mode: (add-hook 'enh-ruby-mode-hook 'inf-ruby-minor-mode) Installation via ELPA interface does the above for you automatically. Additionally, consider adding (add-hook 'compilation-filter-hook 'inf-ruby-auto-enter) to your init file to automatically switch from common Ruby compilation modes to interact with a debugger. To call `inf-ruby-console-auto' more easily, you can, for example, replace the original `inf-ruby' binding: (eval-after-load 'inf-ruby '(define-key inf-ruby-minor-mode-map (kbd "C-c C-s") 'inf-ruby-console-auto))