Lessons from the Application of Formal Methods to the Design of a Storm Surge Barrier Control System. M. Chaudron, J. Tretmans, K. Wijbrans. In: J.M. Wing, J. Woodcock and J. Davies (eds.), FM'99 - World Congress on Formal Methods in the Development of Computing Systems, Volume II, pp. 1511-1526. Lecture Notes in Computer Science 1709, Springer-Verlag, 1999. We describe the experience of the industrial application of formal methods in the development of a mission critical system. We give a description of the system that was to be developed and the methods that were employed to realize the high level of reliability that was required. In this paper we will describe which formal techniques were used, how these techniques were used, the influence of formal methods on the development process and recommendations for managing the use of formal methods.