This volume contains the proceedings of the Fourth Biennial Conference on F- mal Methods in Computer-Aided Design (FMCAD). The conference is devoted to the use of mathematical methods for the analysis of digital hardware c- cuits and systems. The workreported in this bookdescribes the use of formal mathematics and associated tools to design and verify digital hardware systems. Functional verification has become one of the principal costs in a modern computer design effort. FMCAD provides a venue for academic and industrial researchers and practitioners to share their ideas and experiences of using - screte mathematical modeling and verification. Over the past 20 years, this area has grown from just a few academic researchers to a vibrant worldwide com- nity of people from both academia and industry. This volume includes 23 papers selected from the 47 submitted papers, each of which was reviewed by at least three program committee members. The history of FMCAD dates backto 1984, when the earliest meetings on this topic occurred as part of IFIP WG10.2.