Sudoku is a number puzzle played on a 9×9 grid divided into nine smaller 3×3 boxes. The goal is to fill every empty square with digits from 1 to 9 so that each row, each column, and each 3×3 box contains all nine digits exactly once. No math is involved: you solve it through logic and careful observation.

A typical puzzle starts with some numbers already filled in as clues. You study these clues to figure out which numbers must go in the empty squares. If you see that a row already has a 7, you know no other square in that row can be a 7. By applying this kind of reasoning over and over, you gradually fill in the grid.

The puzzle was invented in the 1970s by American architect Howard Garns, who called it “Number Place.” It became wildly popular in Japan in the 1980s, where it got its current name. Today, you'll find sudoku puzzles in newspapers, puzzle books, and apps worldwide. Expert solvers can complete difficult puzzles in minutes, though beginners might need an hour or more. Either way, the satisfaction comes from using pure logic to crack a puzzle that seemed impossible at first glance.