Non-alcoholic fatty liver disease (NAFLD) constitutes a common pathological condition of the liver, the prevalence of which is currently increasing in western countries. NAFLD is frequently diagnosed in males and its incidence is higher in individuals with type 2 diabetes mellitus and obesity. Hence, the disease is considered to be the hepatic manifestation of the metabolic syndrome. A multitude of interconnected risk factors have been described over the years – genetic, hormonal and nutritional, which play important roles in the development of NAFLD. Insulin resistance is considered to be the central pathophysiological condition that promotes the disease in diabetic patients, whereas dyslipidemia and cardiovascular comorbidities (arterial hypertension, ischaemic heart disease) are frequently associated conditions. Although there are currently numerous pathophysiological mechanisms involved in NAFLD that are still unknown or poorly understood, there has been some advancements concerning the pathogenesis of the disease and its progression towards its severe form, known as non-alcoholic steatohepatitis (NASH). In the absence of a clear diagnosis and carefully controlled treatment, NAFLD/NASH may evolve towards liver cirrhosis, liver failure or hepatocellular carcinoma. However, the disease may also generate systemic effects, including the development of chronic kidney disease (CKD). The diagnosis of NAFLD/NASH is based both on its clinical manifestations, revealed by a carefully conducted patient history and physical examination of the patient, and on other investigations; histopathological findings upon liver biopsy, liver ultrasonography and the use of transient elastography (or FibroScan) are some of the most important investigations in NAFLD/NASH. The understanding of the most important risk factors and pathogenic mechanisms of the disease is fundamental for the elaboration of the most efficient treatment, to prevent chronic liver disease or the development of hepatocellular carcinoma.