Acute liver failure (ALF) and acute-on-chronic liver failure (ACLF) are diseases with a rapidly progressive course and high mortality. Apart from treating the underlying triggers and intensive care measures, there are very limited therapeutic options for either condition. Liver transplantation is often the only life-saving treatment, but it cannot always be employed due to contraindications and severe disease progression. ACLF is characterized by underlying liver cirrhosis and typical triggers such as bacterial infections, bleeding, or alcohol binges. ALF occurs in previously healthy livers, usually as a result of purely hepatotoxic events. Disease differences are also reflected in the course and regulations of liver transplantation. Newer prognostic parameters and prioritization programs for ACLF can help improve both waiting list mortality and outcomes after transplantation.