Nonalcoholic fatty liver disease (NAFLD) is recognized as an important cause of chronic liver disease worldwide. NAFLD is the hepatic manifestation of metabolic syndrome and is strongly associated with metabolic conditions including central obesity, insulin resistance, dyslipidemia, and hypertension. NAFLD progression is related to the histologic subtype of Non-alcoholic Steatohepatitis (NASH). An estimated 15-20% of patients with NASH may progress to advanced stages of fibrosis. Many steps in the pathogenesis of NAFLD and NASH are ill defined, but insulin resistance and adipokines apparently play predominant roles. Because effective treatments for NASH are yet to be developed, several potentially promising treatment approaches are under investigation. This issue of Clinics in Liver Diseases presents the views of several internationally renowned NAFLD experts on the most up to date epidemiology, natural history, diagnosis, pathogenesis, and treatment of NAFLD. Additionally, this issue presents recent work on to the importance of NAFLD in children as well as in the individuals who undergo weight reduction surgery. Finally, experts discuss the role of new technologies, such as genomics and proteomics, in understanding NAFLD and developing new biomarkers, including fibrosis markers.