Public expertise in safety, security and environment is a process that is increasingly submitted to control and transparency. It therefore requires an oversight, a monitoring and an aiding approach on its conduct and its governance. Difficulties learned from experiences in framing risk problems and sharing expertise conclusions and recommendations are pointed. Our practice of expertise has made clear to us that "expertise is a decision aiding process for a decision-maker which contains other decision aiding processes for the experts involved. To overcome this paradox, we argue on the need of a generic integrated framework for expertise that allows framing a valid and a legitimate expertise process and conclusions. Public expertise is then defined and main