These European Resuscitation Council (ERC) Guidelines 2025 on Special Circumstances in Resuscitation are based on the 2025 Consensus on Science with Treatment Recommendations (CoSTR) of the International Liaison Committee on Resuscitation (ILCOR), reviews by the expert writing group and relevant peer-reviewed literature. The guideline chapter provides guidance for laypeople and healthcare professionals on the modifications required to basic and advanced life support in adults for the prevention and treatment of cardiac arrest for in-hospital and out-of-hospital cardiac arrest. The ERC Guidelines 2025 Paediatric Life Support cover the special circumstances in children.