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...