Structure and Interpretaition of Computer Program is often considered one of the greatest books written on LISP or generally program structure (as the name suggests). Strangely enough the book is now available freely (through MIT) at: http://mitpress.mit.edu/sicp/full-text/book/book.html One of my favorite quotes happens to be written in the Preface section of the first edition of this book: “Programs must be written for people to read, and only incidentally for machines to execute.”