The production of marine molluscs is an important part of the European aquaculture. Its growth has unfortunately been hindered over the recent years by mortality events, linked to pathogen organisms. Surveillance of mollusc diseases in Europe includes active surveillance of regulated pathogens and non-regulated pathogens and passive surveillance based on mortality reports. However, mortality reporting relies on the good will of producers/fishermen and mostly concerns the Pacific cupped oyster Crassostrea gigas. Since these last years, implemented surveillance programmes have allowed for better defining of the geographic distribution of some mollusc pathogens. This is the case of Bonamia exitiosa, a protozoan parasite previously considered exotic to Europe and which has been detected in different European countries since 2008. Moreover, these different active and passive surveillance programmes have contributed to characterising new pathogens including the protozoan parasite Marteilia cochillia in cockles in Spain and parasites of the genus Mikrocytos in France, Spain, The Netherlands and United Kingdom. Transfer of animals and depuration centers seem to contribute to the spread of mollusc pathogens. However, the source of these apparently new pathogens is often difficult to identify.