Increased UV-B radiation (280 – 315 nm) reaching the surface of the Earth due to decreased ozone layer thickness raised concerns about the effects of this most deleterious part of solar radiation on primary producers. Among these effects are damage to the photosynthetic apparatus, DNA and other cellular targets. Since UV-B in the solar spectrum has been present during the course of evolution, mechanisms for avoidance as well as adaptation have been developed by algae. These include avoidance by staying in protected habitats like the upper layers of soil, repair of UV-induced damage and the synthesis of UV-absorbing compounds such as mycosporine-like amino acids (MAAs). The latter approach is widespread in aquatic as well as terrestrial algae. This review will focus on the chemical nature of UV-absorbing compounds in algae, their distribution among different genera and their ecological implications.