Sudoku is an ancient puzzle that's taking the world by storm. Our Sudoku Resource Center focuses on the enormous amount of free Sudoku content available online, as well as some for-sale items. Are you wondering what singles, hidden singles, locked candidates, naked pairs, triples, quads, and hidden pairs are? Start your search here for downloads, tutorials, books (some for children), e-books and more that will help you master the game. Trace the history of Sudoku from its origin in the eighth century through modern times. Download free Sudoku puzzles at various levels of difficulty, enter daily game contests to win Sudoku books, get a daily Sudoku puzzle to post on your Web site. Get great beginner's resources—learn the rules of Sudoku, receive hints on solving sample puzzles, learn the best solution strategies, and get free Sudoku solvers—just type in the puzzle from your newspaper or favorite Sudoku site and get an immediate solution; some even provide detailed step-by-step explanations. Get mobile-device Sudoku games that can be installed on cell phones, Palm devices, Game Boy players and Java-enabled devices. Some sites have timers, signal when an incorrect number is placed, and provide hints. Purchase T-shirts and coffee mugs with Sudoku puzzles on them, participate in Sudoku player forums, get blank Sudoku worksheets that can be printed out and check out hand-held Sudoku game players—one offers a million puzzles at five levels of difficulty. Download free Sudoku puzzle maker software. And not for the faint of heart—try fiendishly difficult Sudokus with tricky twists, a circular Sudoku and a variant of the puzzle with five interlocking grids.