Guy Steele. Common Lisp: The Language. Digital Press. ISBN 1-55558-041-6. 1990.

The reference manual for Common Lisp, also available online in its entirety. This is very much a reference manual and not a tutorial, but having said that it’s a lot more accessible than many such documents.

It’s remarkable that Common Lisp’s standard has been stable for over thirty years, despite enormous advances in Lisp practices in that time. It shows the care that went into the original standardisation process, but also the effects of some detailed technical choices and (especially) the use of macros in preference to new core mechanisms.

However, it has to be said that the standard also fixed in place certain choices that now seem questionable. It’s a matter of opinion, of course, but personally I think the questionable set includes at least: multiple-value returns and binds, which are unnecessary when you can return lists and destructure them and that impinge on the minimalism of the core language; and allowing symbols to be bound simultaneously to values and functions, which unnecessarily treats the two differently (and for which reason it was removed from Scheme).