• Two big puzzles on each page give you plenty of space to note candidates and sturdy paper holds up well to erasing.
• Extra wide center margins make it easier to solve the puzzles when you fold the book back.
• Large print on white paper is very easy to read (even in dim light).
• Each puzzle has one solution - provided at the back of the book. Go ahead and peek if you get stuck or want to verify your answer.

Caution - These puzzles are harder than the "hard" Sudoku you may have found in newspapers, online or in other Sudoku books. These require advanced logic techniques to solve, like X-Wing, XY-Wing, XYZ-Wing, XY-Chains and Coloring Chains. To see these techniques, click How To Solve Sudoku and scroll down to Puzzle 12. You can also try similar hard puzzles in our free printable book, to see if they are right for you. Just click the green "Join the Preferred Puzzlers" button at the top of the page to get your free copy.