This volume contains the proceedings of Formal Methods 2005, the 13th InternationalSymposiumonFormalMethodsheldinNewcastleuponTyne, UK, during July 18 22, 2005. Formal Methods Europe (FME, www.fmeurope.org) is an independent association which aims to stimulate the use of, and research on, formal methods for system development. FME conferences began with a VDM Europe symposium in 1987. Since then, the meetings have grown and have been held about once every 18 months. Throughout the years the symposia have been notablysuccessfulinbringingtogetherresearchers, tooldevelopers, vendors, and users, both from academia and from industry. Formal Methods 2005 con?rms this success. We received 130 submissions to the main conference, from all over the world. Each submission was carefully refereed by at least three reviewers. Then, after an intensive, in-depth discussion, the Program Committee selected 31 papers for presentation at the conference. They form the bulk of this volume. We would like to thank all the Program Committee members and the referees for their excellent and e?cient work. Apart from the selected contributions, the Committee invited three keynote lectures from Mathai Joseph, Marie-Claude Gaudel and Chris Johnson. You will ?nd the abstracts/papers for their keynote lectures in this volume as well. AninnovationfortheFM2005programwasapaneldiscussiononthehistory of formal methods, with Jean-Raymond Abrial, Dines Bjorner, Jim Horning and Cli? Jones as panelists. Unfortunately, it was not possible to re?ect this event in the current volume, but you will ?nd the material documenting it elsewhere (see the conference Web page).