Wilson disease (WD) is caused by ATPase copper-transporting beta (ATP7B) mutations and results in copper toxicity in liver and brain. Although the defective gene was identified in 1993, the specific mechanisms underlying copper toxicity and the remarkable phenotypic diversity of the disease are still poorly understood. Animal models harboring defects in the ATP7B homolog have helped to reveal new insights into pathomechanisms of WD. Four rodent models with ATP7B gene defects have been described - the Long-Evans Cinnamon (LEC) rat, inbred mouse models (toxic milk (tx), the Jackson Laboratory toxic milk (tx-j)), and the genetically engineered ATP7B-/- (knockout) mouse - all of which develop liver disease to different extents. Copper accumulation in parts of the brain accompanied by some neurologic involvement was revealed in LEC rats and tx/tx-j mice, but the pathology is less severe than human neurologic WD. Several dogs show hepatic copper toxicity resembling WD; however, brain involvement has not been observed and the underlying genetic defect is different. These models are of great value for examination of copper distribution and metabolism, gene expression, and investigation of liver and brain pathology. The availability of disease models is essential for therapeutic interventions such as drug, gene, and cell therapy. Findings made by animal studies may facilitate the development of specific therapies to ameliorate WD progression.