The objective of the game is to fill all the blank squares in a game with the correct numbers. There are three very simple constraints to follow. In a 9 by 9 square Sudoku game:

• Every row of 9 numbers must include all digits 1 through 9 in any order
• Every column of 9 numbers must include all digits 1 through 9 in any order
• Every 3 by 3 subsection of the 9 by 9 square must include all digits 1 through 9

Similarly, smaller Sudoku puzzles, such as the 4x4 puzzle, must have the numerals 1 through 4 in each row, column and subsection. Larger Sudoku games (16 by 16) must have numerals 1 through 16 in each row, column and region. The principles are the same whatever the size of the game.

Every Sudoku games begins with a number of squares already filled in, and the difficulty of each game is largely a function of how many squares are filled in. The more squares that are known, the easier it is to figure out which numbers go in the open squares. As you fill in squares correctly, options for the remaining squares are narrowed and it becomes easier to fill them in. The Sudoku games on SudokuDaily.net let you check your progress as you go, to help prevent going down a wrong path.