While classic 9x9 Sudoku is the most popular, there are many exciting variations that add new challenges and solving techniques.
Killer Sudoku
In Killer Sudoku, numbers in outlined regions must sum to the given total. This adds mathematical constraints to the puzzle.
Samurai Sudoku
Five overlapping 9x9 grids create a complex puzzle where the center grid shares rows and columns with the four corner grids.
Diagonal Sudoku
In addition to rows, columns, and boxes, the two main diagonals must also contain all numbers 1-9.
Irregular Sudoku
Instead of 3x3 boxes, irregular regions of nine cells each must contain all numbers 1-9.
Windoku
Four additional 3x3 regions (windoku regions) must also contain all numbers 1-9.