This is an Enstti Training course. The training will start by the overview of decommissioning aspects and the presentation of ongoing decommissioning projects (NPPs and fuel cycle facilities). This will ensure that all participants share the same understanding of decommissioning and will set the scene for the further lectures. Second day will start with the presentation of the methodologies for safety assessment and regulatory review of safety assessment implemented in France. This will be the starting point for lectures point for lectures performed by specialists addressing the risks identification, human factors, radiation protection, fire safety, risks linked to handling activities during decommissioning and radiological characterisation vs waste management. To illustrate how to deal with these issues, a test case in radiation protection during decommissioning will be proposed to the participants. In addition, during this training, a specific session will be dedicated to innovative techniques for decommissioning related to 3D simulation and contaminated site characterization with geostatistics concepts.