 Whereas there are several validated systems for reporting postoperative complications, there are only a few and not prospectively validated systems for reporting intraoperative complications. The investigators developed a definition and CLASSification for Intraoperative Complications CLASSIC within a Delphi study involving international interdisciplinary experts. As both surgery and anaesthesia may be involved in complications in the perioperative period, all patient-related intraoperative complications occurring between skin incision and closure are considered in this reporting system. 