Emacs includes a book, or maybe it's in the list of installable packages called An Introduction to Programming in Emacs Lisp (I think the package is called 'ein

Emacs includes a book, or maybe it's in the list of installable packages called An Introduction to Programming in Emacs Lisp (I think the package is called 'eintr') that does a pretty good job as an introductory lisp programing text and then gets deeper into the internal functions of Emacs. By the later part of it I felt like I had a decent handle on Emacs Lisp and could read the code for packages I was interested in reasonably well.