Sudoku is a logic-based number placement puzzle. The objective is to fill a 9x9 grid so that each column, each row, and each of the nine 3x3 boxes called regions, contain the digits from 1 to 9. Each book contains puzzles with increasing levels of difficulty—kids’ stuff, easy, medium, difficult and expert level. Sudoku is easy to learn but a challenge to master. Spend a few minutes familiarizing yourself with the rules of this number puzzle and you’ll be ready for hours of fun.