Amongst the diversity of methods used by organisms to reduce damage caused by ultraviolet (UV) radiation,
the synthesis of UV-screening compounds is almost ubiquitous. UV-screening compounds provide a passive
method for the reduction of UV-induced damage and they are widely distributed across the microbial, plant
and animal kingdoms. They share some common chemical features. It is likely that on early earth strong
selection pressures existed for the evolution of UV-screening compounds. Many of these compounds probably
had other physiological roles, later being selected for the efficacy of UV screening. The diversity in
physiological functions is one of the complications in studying UV-screening compounds and determining
the true ecological importance of their UV-screening role. As well as providing protection against ambient
UV radiation, species with effective screening may also be at an advantage during natural ozone depletion
events. In this review the characteristics of a wide diversity of UV-screening compounds are discussed and
evolutionary questions are explored. As research into the range of UV-screening compounds represented in
the biosphere continues, so it is likely that the properties of many more compounds will be elucidated. These
compounds, as well as providing us with insights into natural responses to UV radiation, may also have
implications for the development of artificial UV-screening methods to reduce human exposure to UV
radiation.