Acute Liver Failure (ALF) still presents high mortality rates, and liver transplant is the only treatment with proven efficacy. However transplant is not always possible and systems for Extracorporeal Liver Support (ELS) are being developed which can treat patients with ALF, for whom a transplant is not available, or is delayed. They can also treat patients with chronic liver disease who develop ALF. There are two types of ELS: artificial systems (hemoperfusion, plasmaperfusion, therapeutic plasma exchange, continuous hemodialysis and high volume continuous hemofiltration) and bioartificial systems. These are based on a biological component (animal or human hepatocytes) inserted into a bioreactor, whose main function is to perform the metabolic activity and synthesis that the liver can no longer perform. The results obtained in clinical trials have so far shown that the best results in terms of compensating for lost metabolic function and detoxification are obtained inserting artificial components in the bioartificial circuit.