During the last few decades, there has been considerable concern over the depletion of stratospheric ozone as a result of anthropogenic pollutants. This has resulted in a concomitant increase in solar ultraviolet-B radiation (280-320 nm). High levels of UV-B radiation are responsible for multiple biologically harmful effects in both plants and animals. Many different plant responses to supplemental UV-B radiation have been observed, mostly injurious but sometimes beneficial. UV-B can influence plant processes either through direct damage or via various regulatory effects. In plants, direct effects include DNA damage, membrane changes and protein denaturation, which often cause heritable mutations affecting various physiological processes, including the photosynthetic apparatus. These could adversely affect plant growth, development and morphology, especially the productivity of sensitive crop species. This paper reviews the current knowledge about the plant physiological responses to UV-B stress.