The paper reviews growth chamber, greenhouse, and field studies on the effects of ultraviolet B (UV-B, between 280 and 320 nm) radiation on agricultural crop plants. The understanding of the physiological effects of UV-B radiation comes primarily from growth chamber studies where UV-B is artificially supplied via filtered lamps. Both photosystems I and II, as well as carboxylating enzymes, are sensitive to UV-B radiation. Ultraviolet B radiation also affects stomatal resistance, chlorophyll concentration, soluable leaf proteins, lipids, and carbohydrate pools. In general, the effects of UV-B radiation are accentuated by the low levels of visible radiation typically found inside growth chambers. Ultraviolet-B radiation has also been shown to affect anatomical and morphological plant characteristics. Commonly observed UV-B induced changes include plant stunting, reductions in leaf area and total biomass and alterations in the pattern of biomass partitioning into various plant organs.