The objective of this project was to survey the main accident investigation methods that have been developed since the early or mid-1990s. The motivation was the increasing frequency of accidents that defy explanations in simple terms, for instance cause-effect chains or “human error”. Whereas the complexity of socio-technical systems is steadily growing across all industrial domains, including nuclear power production, accident investigation methods are only updated when their inability to account for novel types of accidents and incidents becomes inescapable. Accident investigation methods therefore typically lag behind the socio-technological developments by 20 years or more.