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Chromium has two naturally occurring valence states, trivalent [Cr(III)] and hexavalent [Cr(VI)]. Cr(VI) is known carcinogen, while Cr(III) is considered generally safe at exposure concentrations. Cr(III) is nontoxic due to its poor absorption by mammalian cells due to its inability to cross the plasma membrane. Both Cr(VI) and Cr(III) produce reactive oxygen species (ROS) by producing hydroxyl radicals through a Haber–Weiss reaction. Cr(III) plays an important role in the Cr(VI) carcinogenic mechanism as Cr(VI) is reduced to Cr(III) inside the cell. Cr(III) can then bind/interact with DNA and proteins and cause cellular dysfunctions. It is established that the ROS produced by Cr(VI) are key to its carcinogenic mechanism. In this chapter, we detail the ROS produced by chromium. We briefly discus the role of ROS and Cr(III) in Cr(VI) carcinogenesis. Lastly, we focus on the potential toxicity of Cr(III) compounds and highlight …