The aetiology of chronic liver disease covers a wide range of congenital or acquired abnormalities of the hepatocellular biochemical network. Although our knowledge has considerably increased in recent years, the aetiology of chronic liver disease often remains obscure. Acquired irreversible disturbances of normal liver function can be mediated by hepatotrophic viruses, chemicals, chronic oxygen depletion, or interference with the immune system. Considerable progress has been made in the detection and characterisation of hepatitis B, C, and D viruses as causative agents of chronic active hepatitis. Alcohol abuse remains the predominant cause of chronic liver disease in the Western world. The targets of autoantibodies used to diagnose autoimmune diseases of the liver and primary biliary cirrhosis continue to be biochemically defined. Their significance for the aetiology of the disease, however, remains to be established. Nonparenchymal cells play an important role in the sequence of events following hepatocellular injury and ultimately leading to liver cirrhosis. They release vasoactive compounds, cytokines, and other important mediators, and participate in the modulation of the extracellular matrix that is characteristic of liver fibrosis and cirrhosis. The biochemical basis of liver cell necrosis remains poorly defined. In spite of recent progress, and the detection of some new pathogenic principles that help in the understanding of the complications of chronic liver disease such as portal hypertension, oesophagogastric variceal bleeding, portosystemic encephalopathy, ascites, and other metabolic disturbances, many questions concerning the aetiology and pathophysiology of chronic liver disease and its complications remain to be answered.