Nonalcoholic fatty liver disease (NAFLD) is tightly associated with obesity and the metabolic syndrome in the United States and other Western countries. It is also the liver disease most rapidly increasing in prevalence in the United States, and has become a major indication for liver transplantation worldwide. Compelling evidence shows that the degree of liver fibrosis dictates liver prognosis in NAFLD. This review focuses on fibrosis based on clinical and basic perspectives. The authors summarize the physiopathology of fibrosis development and progression in NAFLD, highlighting its molecular mechanisms, clinical consequences of fibrosis, the diagnostic approach and management strategies.