Formal methods are mathematically-based techniques, often supported by reasoning tools, that can offer a rigorous and effective way to model, design and analyze computer systems. The purpose of this study is to evaluate international industrial experience in using formal methods. The cases selected are representative of industrial-grade projects and span a variety of application domains. The study had three main objectives: To better inform deliberations within industry and government on standards and regulations; To provide an authoritative record on the practical experience of formal methods to date; and A To suggest areas where future research and technology development are needed. This study was undertaken by three experts in formal methods and software engineering: Dan Craigen of ORA Canada, Susan Gerhart of Applied Formal Methods, and Ted Ralston of Ralston Research Associates. Robin Bloomfield of Adelard was involved with the Darlington Nuclear Generating Station Shutdown System case. Support for this study was provided by organizations in Canada and the United States. The Atomic Energy Control Board of Canada (AECB) provided support for Dan Craigen and for the technical editing provided by Karen Summerskill. The U.S. Naval Research Laboratories (NRL), Washington, DC, provided support for all three authors. The U.S. National Institute of Standards and Technology (NIST) provided support for Ted Ralston.