Current research on chromium (Cr) ecotoxicity primary focuses on the adverse effects of Cr(VI). Concerns about high levels of Cr(III) in the environment are mostly driven by its possible (re)oxidation to the highly toxic hexavalent form, but trivalent chromium is considered of limited ecotoxicological relevance. However, Cr(III) can also elicit a large range of responses in aquatic and terrestrial plants including inhibition of growth and seed germination, damage to chloroplasts, reduced photosynthesis, oxidative stress, and alteration of nutrient balance, organelles and cellular function. Furthermore, most studies pay little if any attention to the complex chemistry of Cr(III) in the ecotoxicological test media used in controlled laboratory studies. In particular, Cr(III) can rapidly undergo hydrolysis that transforms soluble Cr 3+ ions into Cr oxy-hydroxides-Cr(OH)3. Given the very low theoretical solubility of Cr(OH)3 (about 5 µg/L), their formation can markedly decrease the Cr(III) levels to which test organisms are actually exposed during the tests. These phenomena make comparison among studies far from straightforward and question the validity of many concentrations vs. response relationships reported for Cr(III). Although the high ecotoxicity of Cr(VI) is unquestionable, the critique presented in this chapter suggests that current consensus suffer from a general underestimation of Cr(III) ecotoxicity.