CIDER
The Clojure Interactive Development Environment that Rocks for Emacs
...While clojure-mode supports editing Clojure source files, cider-mode adds support for interacting with a running Clojure process for compilation, debugging, definition and documentation lookup, running tests, and so on. CIDER aims to provide an interactive development experience similar to the one you’d get when programming in Emacs Lisp, Common Lisp (with SLIME or Sly), Scheme (with Geiser), and Smalltalk. Programmers are expected to program in a very dynamic and incremental manner, constantly re-evaluating existing Clojure definitions and adding new ones to their running applications. You never stop/start a Clojure application while using CIDER - you’re constantly interacting with it and changing it.