Liver diseases are many and can often be difficult to diagnose, because symptoms can be vague and easily confused with other health problems. However, physicians can be helped by specific markers used to diagnose and follow up liver diseases. In fact some of the enzymes and the end products of the metabolic pathway occurring in the liver are very sensitive for the abnormality occurred and, for this reason, may be considered as biochemical markers of liver dysfunction. In this chapter, we will examine the main markers of liver diseases, dividing them as markers of hepatic necrosis, markers of hepatic obstruction, markers of liver’s biosynthetic capacity, markers of hepatic steatosis, markers of hepatic fibrosis, and markers of hepatic tumor.