While ozone has been shown to be the most important air pollutant affecting national crop production in North America and western Europe, mainly because it is found at phytotoxic concentrations over large areas, its impact in the developing countries of Asia, Africa and Latin America, where the economic and social consequences of loss of production may be much greater, is uncertain. This review assesses the current and future significance of ozone impacts on agriculture in these countries. Although the information available on rural ozone concentrations is very limited, it does show that these concentrations can be high enough to have adverse effects on sensitive species, while a limited number of experimental studies have shown decreases in yield of staple crops due to ambient ozone. Current projections of rising emissions of ozone precursors suggest that the impacts on agriculture may increase very rapidly over the next two decades. There is an urgent need for more rural studies to determine ozone concentrations, and their impact on major crop species, in order to assess the current scale of the problem, and to develop models to estimate the future impacts of increased emissions.