Lisp is a (family of) general purpose functional programming language(s), based on the lambda calculus, and with the ability to manipulate source code as a data structure.
Introduction
The name LISP derives from "LISt Processing". It was originally created as a practical mathematical notation for computer programs. See wikipedia for more information.
Hello World Program in Lisp
;;; Hello World in Common Lisp
(defun helloworld ()
  (print "Hello World!"))
Popular dialects
Free Lisp Programming Books
- Common Lisp the Language, 2nd Edition
 - Common Lisp: A Gentle Introduction to Symbolic Computation - David S. Touretzky
 - Common Lisp Quick Reference
 - Let Over Lambda - 50 Years of Lisp
 - Natural Language Processing in Lisp
 - On Lisp
 - Practical Common Lisp
 - Successful Lisp: How to Understand and Use Common Lisp - David Lamkins
 - Sketchy LISP - Nils Holm