Acute liver failure is a complex multisystemic illness that evolves quickly after a catastrophic insult to the liver leading to the development of encephalopathy. The underlying aetiology and the pace of progression strongly influence the clinical course. The commonest causes are paracetamol, idiosyncratic drug reactions, hepatitis B, and seronegative hepatitis. The optimal care is multidisciplinary and up to half of the cases receive liver transplants, with survival rates around 75%–90%. Artificial liver support devices remain unproven in efficacy in acute liver failure.