This workshop, held in Pavia, Italy on 4-6 February 2015, was the fourth in a series of NEA meetings (Tokyo, Japan, August 1999, Jeju, Korea, November 2006, Lyon, France, April 2008), dedicated to probabilistic approach of seismic hazard or seismic risk. The main objectives were to foster exchanges between earth scientists, statisticians and engineers so as to share experiences in progress related to developments in testing the results of probabilistic seismic hazard analyses (PSHA) with special focus on assessing the benefits of using Bayesian techniques for such a purpose. The goal was to address the current status of the regulatory arena, identifying and recommending good practices for member countries and exploring R&D to be developed on this topic.