Created in the United States, these intriguing conundrums were originally called Number Place puzzles. Their recent rise in popularity began in Japan, where the name translated as sudoku. Here we've indicated the skill level necessary to complete each sudoku book in this series in the same way Japanese karate levels are ranked: by different colored belts. This is the Black Belt volume, filled with puzzles that will provide a sly, absorbing test for even the best, most proficient experts.

It's impossible to complete only one sudoku at a time, because solving them is habit-forming!