While the human eye can practically cope only with two aspects of light, brightness and colour, many animals use polarization as a further source of visual information. The text starts with an introduction into imaging polarimetry, an efficient technique for measuring light polarization, and moves onto a description of the various polarization patterns occurring in nature, such as celestial polarization. The major part of the book is dedicated to the fascinating question: How do animals use polarization patterns? Following a compendium of the physiology of polarization sensitivity, several case studies are presented, such as honeybees or ants using polarized light as a compass or aquatic animals orientating by the underwater polarization. Further, it is explained how man-made objects affecting the natural optical environment may disorientate animals. For instance, as in the case where oil or glass surfaces can be more attractive for water-seeking polarotactic insects than the water surface.