Ebook: An Introduction to Programming in Emacs Lisp

A very good introduction to using elisp. I have about a decade of experience programming and extending Emacs; I picked this up to consider giving it to my computer science students. I finally decided against it only because Successful Lisp is such an amazing book. No, really, I cannot recommend Successful Lisp highly enough.

This book is very good and focuses on the specifics of Emacs Lisp. If you are interested in extending that venerable editor, this is a good place to start. If you are interested in learning programming in Lisp (specifically Common Lisp), take a look at Successful Lisp.