Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases. The con- cept of NAFLD ranges from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) and cirrhosis. The majority of NAFLD has been recognized as a hepatic manifestation of metabolic syndrome with a close association with insulin resistance. Regarding the development of NAFLD/NASH, adiponectin and TNFa are thought to have key roles. Moreover, the gut microbiota may affect energy metabolism in the context of NAFLD. Genetic susceptibility to NAFLD may be determined by polymorphisms of patatin-like phospho- lipase domain-containing 3 (PNPLA3) and methylenetetrahydrofolate reductase (MTHFR). The diagnosis of NAFLD/NASH is made by liver biopsy. The differential diagnosis between NAFL and NASH has been made according to Matteoni's classification, and the progression of liver fibrosis has been determined by Brunt's staging. For the prevention and treatment of NAFLD, the modification of dietary habits and promo- tion of physical activity including aerobic and resistance training are essential. Although vitamin E, pioglita- zone, or liraglutide is used as a first-line treatment for NAFLD, pharmacotherapy for NAFLD has not been established because of the insufficient pharmacological effects of these agents. Among recently developed drugs, farnesoid X nuclear receptor ligand obeticholic acid is the most promising for first-in-class treatment of NASH. In this review, the details of recent advances in knowledge about the epidemiology, etiology, diag- nosis, and treatment of NAFLD/NASH are described. [Review].