This article aims to describe how it would be possible to use the Yourdon Structured Method (YSM) and Vienna Development Method (VDM) together during the system development lifecycle, and the advantages of this approach. It outlines the basic principles of both methods, discussing the relative merits and disadvantages of each, and suggests why using them together may prove to be useful when building systems which demand proof of correctness. A development process which incorporates the two methods is presented, showing how the two approaches fit naturally together. Also the use of YSM state-transition diagrams to model aspects of control within VDM is discussed. In conclusion, the benefits of using the two notations are discussed, and areas are identified in which further research and development is needed.