This final chapter highlights the advances and some of the unanswered questions concerning bovine virus diarrhoea virus (BVDV) presented in this Review by specialists from around the world. Persistently viraemic cattle play an essential role in the dissemination of BVDV but it is suggested that acute infections with the virus are also important. The role of latency is considered but, as yet, there is no evidence that it plays a part in pathogenesis. It is well established that BVDV, Border disease virus and hog cholera virus infect sheep and pigs. There is also some indication that pestiviruses may be involved in other infections of ruminants, such as syndrome X and hyena disease. They also infect other ruminants, such as deer, and human infections have been reported. It is now known that the pathogenesis of mucosal disease is due to the combined action of the two BVDV biotypes. However, the cause of death remains an enigma. It is suggested that, due to the importance of this syndrome, it may be an appropriate time to reconsider the use of "mucosal disease virus" to replace the ungainly name "BVDV".