What you need to know about sudoku: Sudoku is a game of logic, based on a grid of 9 columns and 9 rows. This is sub-divided into nine 3 x 3 squares. A completed Sudoku puzzle comprises this grid completely filled with the numbers 1 - 9 appearing exactly once in each row, column and square. You can see an example grid to the right. Another thing about sudoku - as you go through solving it, you will need pencilmarks to keep track of what goes where, these are shown by the small numbers to the right. Each Sudoku puzzle, or at least each valid puzzle, has one unique solution. The difficulty varies depending on how many numbers you are given to start with - the more numbers usually the easier the puzzle. Puzzles also tend to be symmetrical. Another thing about sudoku - you should be able to use logic to solve each puzzle and never need to make a guess and hope for the best! This is achieved by implementing 'human solve algorithms' in the puzzle generators (or making them by hand). From the starting grid, you should be able to deduce the number that must go in every square of the grid, number by number. You should not have to guess at any values if the grid has been correctly generated. There are a number of simple strategies that you can use to help you solve the Sudoku grid. So that's all you need to know about sudoku, now it is time to start playing! We have literally hundreds of sudoku puzzles for you to play at our online Puzzle Club, across many different genres of the puzzle including some variants you may not have come across before.