Pro-oxidants are numerous and varied. Antioxidants are equally varied in their mechanism of action, and oxidative stress is likely not a simple arithmetic summation of these two opposing forces. More likely, it is a complex set of interrelated formulas with large areas of overlap and small areas of unique effect. In this article, the language of oxidative stress is reviewed, the consequences of oxidative stress are presented, the pathophysiology of oxidative stress in the liver is briefly discussed, and various antioxidant treatment options most relevant to small animal patients with liver disease are reviewed.