In contrast to ANSI Common LISP, which I just reviewed, Peter Siebel's upcoming book, Practical Common Lisp will cover CLOS in some detail. Peter has been writing his book since late last year and has been putting chapters up on the web for public comment as he completes them. Peter's chapters were one of the first web resources I found when I started learning CL and they have earned a spot in my Links for Newbies over there on the side of the blog page (for those not reading on an aggregator). In any case, check out Peter's book and be sure to tell him what you think of the chapters now so the book is solid when it arrives. Then, when it arrives, be sure to buy a copy. (For what it's worth, I have written three books previously and it's very hard work. You need all the moral support you can find. The hours are long and the pay is horrible. Even a pat on the back can make a big difference.)