78 Degrees of Wisdom is an invaluable resource in my opinion. It trully explains the Waite deck, and in doing comparitive study with other decks it has helped me identify common threads or other elements. IMHO a Tarot library cannot be complete without this book. If you would like to get a better idea about the book you can go to the Study Group Forum and see the work we have done using 78 DW as the basis.