Sudoku is a puzzle involving numbers with the essence that each number appears only once in each line and row of a grid. The standard Sudoku is a 9×9 grid that consists of nine 3×3 sub-grids. The puzzler needs to place numbers from one to nine into the blanks of a grid to complete the puzzle following certain rules. It is a logic-based game, and doesn't require a high educational level.

Modern Sudoku first appeared as a game called Number Place in the U.S. magazine Math Puzzles and Logic Problems in the 1970s. In 1984, it was introduced to Japan and soon became popular among people with the Japanese name "Sudoku." The game is easy to promote because people can play it with only a piece of paper and a pencil. Many newspapers and magazines have Sudoku puzzles to attract the attention of readers.

Currently, there are many Sudoku competitions around the world. The largest of them is the World Sudoku Championship (WSC), a top-level annual event sponsored by the World Puzzle Federation. The first WSC was held in the city of Lucca, Italy, in 2006.