Non-alcoholic fatty liver disease (NAFLD) is now the most common cause of liver disease in paediatric population of the industrialized countries. NAFLD ranges from simple fatty liver to non-alcoholic steatohepatitis (NASH) associated with or without fibrosis, which represents the hepatic component of the metabolic syndrome. In fact, the major contribution to NASH development is carried by other comorbidities associated with metabolic syndrome, including obesity, insulin resistance, dyslipidaemia and type 2 diabetes. Even though a genetic background may predispose to NAFLD, the increasing prevalence among children and adolescents is largely due in part to the excessive consumption of refined carbohydrates and saturated fats, and in part to sedentary lifestyle. Therefore, NAFLD may describe several diseases with different presentation and aetiology, and requiring a personalized approach both in the diagnosis and treatment. In this chapter, we review the current concepts that may help paediatricians to better understand and address the NAFLD in child: clinical and histological aspect, risk factors and epidemiology, pathogenesis, diagnosis and treatments of NAFLD.