In the past 100 years, tropospheric ozone concentrations [O3] have more than doubled in response to industrialization. Current [O3] can cause oxidative damage in plants, leading to yield losses that have been estimated to cost growers $1.8-3.6 billion per year for soybean in the US. Models indicate that [O3] will continue to rise another 25% by the year 2050, thus exacerbating the strain on agriculture to provide food at a time of rapid population growth. Here, we compare the O3 response of Glycine max, Pisum sativum, Phaseolus vulgaris, Cicer arietinum and Medicago sativa - all commercially relevant crops, important for global food security. When grown in elevated chronic O3, in situ measurements of stomatal conductance (gs) revealed a broad range of O3 sensitivities. The most sensitive species, P. vulgaris and M. sativa, each had decreases in gs of 55%, while the most tolerant species, P. sativum, was not significantly different from ambient-grown plants. G. max and C. arietinum showed an intermediate response, with decreases in gs of 46% and 36%, respectively. This trend continued for measurements of net CO2 assimilation (A) and chlorophyll fluorescence (PhiPSII), as well as estimates of the maximum Rubisco carboxylation rate (Vc,max) and maximum rate of electron transport (Jmax). Also consistent with the ranges of O3 sensitivity were whole plant characteristics such as leaf longevity, total plant leaf area and biomass, in addition to biochemical markers of antioxidant capabilities such as apoplastic ascorbate. To identify specific markers of O3 tolerance at the molecular level, we have undertaken a transcriptome sequencing approach using the Illumina platform to compare global changes in gene expression between each of the legume species.