Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A Wallpaper group is a mathematical classification of a two-dimensional repetitive pattern, based on the symmetries in the pattern. SUch patterns occur frequently in architecture and decorative art. THere are 17 possible distinct groups. WAllpaper groups are two-dimensional symmetry groups, intermediate in complexity between the simpler frieze groups and the three-dimensional crystallographic groups.