The recognised de®ciency in the level of empirical investigation of software engineering methods is particularly acute in the area of formal methods, where reports about their usefulness vary widely. We interviewed several formal methods users about the use of formal methods and their impact on various aspects of software engineering including the effects on the company, its products and its development processes as well as pragmatic issues such as scalability, understandability and tool support. The interviews are a ®rst stage of empirical assessment. Future work will investigate some of the issues raised using formal experimentation and case studies. q