In the case of an event at a nuclear installation it is important to accurately determine the root causes, in order to allow corrective actions to be implemented to address them and prevent their recurrence. There are different analysis tools, techniques and methods available which can be used to evaluate the root causes of events, and this publication presents a comprehensive reference manual for them and allows organizations to deepen their knowledge of these instruments. In addition, it also provides new organizations with a broad overview of the root cause analysis process. The present manual is also intended to provide guidance to all organizations establishing a new process for root cause analysis, especially in countries embarking upon a nuclear power programme.