This, along with the Ashley Book of Knots, is one of the two "landmark" knot books. It belongs in the library of the serious knot researcher, but should not be the first or even second item in a new collection. That honor must go to Ashley.
This is not a guide for beginners. Most knots are photographed complete and tight, with precious little material on tying steps. Even expert tyers will find some of the photos dificult to follow. Organization is often poor, with knots of completely different appearance and use sometimes on the same page.
On the other hand, the sections on multi-strand knots, splicing, plaits, and decorative knotting are among the finest ever done, but again illlustrated directions are sparse.
Definitely find a copy and take a good look at this book, but make sure it is what you want before purchasing.