Formal methods are coming of age. Mathematical techniques and tools are now regarded as an important part of the development process in a wide range of industrial and governmental organisations. A transfer of technology into the mainstream of systems development is slowly, but surely, taking place. FM’99, the First World Congress on Formal Methods in the Development of Computing Systems, is a result, and a measure, of this new-found maturity. It brings an impressive array of industrial and applications-oriented papers that show how formal methods have been used to tackle real problems. These proceedings are a record of the technical symposium ofFM’99:alo- side the papers describing applications of formal methods, you will ndtechnical reports,papers,andabstracts detailing new advances in formaltechniques,from mathematical foundations to practical tools. The World Congress is the successor to the four Formal Methods Europe Symposia, which in turn succeeded the four VDM Europe Symposia. This s- cession reffects an increasing openness within the international community of researchers and practitioners: papers were submitted covering a wide variety of formal methods and application areas. The programmecommittee reffects the Congress’s international nature, with a membership of 84 leading researchersfrom 38 di erent countries.The comm- tee was divided into 19 tracks, each with its own chair to oversee the reviewing process. Our collective task was a di cult one: there were 259 high-quality s- missions from 35 di erent countries.