The Fourth International Conference on Reliable Software Technologies, Ada- Europe'99, took place in Santander, Spain, from June 7 to 11, 1999. It was sponsored by Ada Europe, the European federation of national Ada societies, in cooperation with ACM SIGAda and Ada Spain, and it was organized by members of the University of Cantabria and the Technical University of Madrid, in Spain. This was the 19th consecutive year of Ada Europe conferences, which have always been the main Ada events in Europe, with their counterparts being the ACM SIGAda conferences in the USA (formerly Tri Ada). The...