Extra tricky. Extra tough. It's the sudoku collection that's not for the faint of heart. If you're craving the challenge, sharpen your pencil and pit your wits against the Japanese puzzle-makers at the top of their game. In each of these more than 300 handcrafted puzzles, ranked by difficulty from expert to x-treme to ultimate, every move is an adventure, a one-on-one challenge with a grandmaster who delights in elegance, symmetry, and building in the occasional roadblock. But keep going. You'll solve it eventually... you genius! Can't get enough? Look for: The Original Sudoku - The Original Sudoku Book 2 - More Original Sudoku  - X-treme Sudoku - Expert Sudoku  - The Original Sudoku Page-a-Day Calendar  Nikoli is the Japanese puzzle and game company that’s been nurturing and developing sudoku for over thirty-five years. They hold the trademark on sudoku in Japan, and supply 100 percent of the puzzles published in Japanese newspapers and magazines.