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,...