Polyominoes will delight not only students and teachers of mathematics at all levels, but will be appreciated by anyone who likes a good geometric challenge. There are no prerequisites. If you like jigsaw puzzles, or if you hate jigsaw puzzles but have ever wondered about the pattern of some floor tiling, there is much here to interest you. A polyomino is a shape cut along the lines from square graph paper; the pronunciation of polyomino begins as does polygon and ends as does domino. Tilings, also called tessellations of mosaic patterns, are older than civilization itself. Tiling with polyominoes provides challenges that range from the popular jigsaw-like puzzles to easily understood mathematical research problems. You will find unsolved puzzles and problems of both kinds here. Answers are provided for most of the problems that have known solutions. It is only fair to repeat here the warning stated in the preface to this book, 'Playing with polyominoes can be habit forming.'