Eijidoku is based on the same principles as sudoku. "Su" means number whereas "Eiji" means letter. The word "doku" means single. The big difference is that Eijidoku is more involved and a lot more fun. Not only do you have to work out the grid, but you also have to find words, sentences, anagrams, etc. from the 9 x 9 grid. Each puzzle is laid out like a Sudoku grid with letters not numbers in the boxes. Once the 9 x 9 grid is completed, the next task is to find the words or anagrams (jumbled up letters that make up a word) in the shaded areas. Inside the book is an A-Z chart to help find the correct letters from the shaded areas. To make it easier and clearer, the book has been printed in a larger size. It is also uniquely spiral bound so that each puzzle lays flat, making it easier to work on.