This book is huge! According to the introduction, it contains 268,000 words which represent an exhaustive list of every valid play in Scrabble. Presumably this is the same as the SOWPODS word list, which contains 267,751 words and is used for tournament play outside of the USA, Canada, Thailand and Israel.
About 75% of this substantial hardback is taken up by words of between two and nine letters in length and includes short definitions. This is invaluable as I think it makes learning words that much easier when you know the definition.
The other 25% of the book is a list of words of between ten and fifteen letters in length. No definitions here but I don't mind as, according to the book, "in any Scrabble game, most words will be between two and nine letters, with longer words being formed only very rarely." As a casual Scrabble player, I think I have some way to go before I start playing 10+ letter words!
In addition to over a quarter of a million words (!), there is a fantastic bonus section called A Quick Guide to Scrabble by Barry Grossman. This section has been lifted straight from Grossman's paperback book, Scrabble: Play to Win, included here in its (almost) entirety. About 80% of that book is included here; it is worth purchasing the paperback for the missing content as it contains additional useful tips and advice. Also, the svelte paperback is easier to carry around than this monster hardback! (See my review of Play to Win for a list of contents).
Collins Ultimate Scrabble Word List is absolutely indispensable to all Scrabble enthusiasts. I intend to keep it close to hand for all my home Scrabble games where it will no doubt come in very handy to resolve any disputes. (For Scrabble games away from home, I have a slightly more portable iPhone app containing the same list of words).
In summary, this has to be the best, most comprehensive Scrabble word list around and I recommend it unreservedly. The book is well laid out and it is easy and quick to look up words. Very good price, too. If you play Scrabble, you NEED this superb book.