The prognosis and management of liver disease greatly depends on the amount of liver fibrosis. Non-alcoholic fatty liver disease (NAFLD), ranging from simple steatosis to non-alcoholic steatohepatitis (NASH), is emerging as a major cause of liver disease in Western countries because of the increasing prevalence of obesity and type 2 diabetes. A key issue in patients with NAFLD is the differentiation of NASH from simple steatosis. It is particularly important to identify NASH patients as they are at greatest risk of developing complications such as cirrhosis, liver failure and hepatocellular carcinoma. The limitations of liver biopsy (invasive procedure, sampling errors, interobserver variability and non-dynamic fibrosis evaluation) have stimulated the search for non-invasive approaches for the assessment of steatosis and liver fibrosis in patients with NAFLD. A variety of methods, including serum markers, imaging techniques such as ultrasound, CT, MRI and measurement of liver stiffness by transient elastography, have been proposed for the non-invasive assessment of steatosis and hepatic fibrosis. This review discusses the advantages and limitations of these different methods in clinical practice.