Since 1995, when the SPIN workshop series was instigated, SPIN workshops have been held on an annual basis in Montr´ eal (1995), New Brunswick (1996), Enschede (1997), Paris (1998), Trento (1999), Toulouse (1999), Stanford (2000), Toronto (2001), Grenoble (2002) and Portland (2003). All but the first SPIN workshop were organized as satellite events of larger conferences, in particular of CAV (1996), TACAS (1997), FORTE/PSTV (1998), FLOC (1999), the World Congress on Formal Methods (1999), FMOODS (2000), ICSE (2001, 2003) and ETAPS (2002). This year again, SPIN was held as a satellite event of ETAPS 2004. The co-location of SPIN workshops with conferences has proven to be very successful and has helped to disseminate SPIN model checking technology to wider audiences. Since 1999, the proceedings of the SPIN workshops have appeared in Springer-Verlag’s Lecture Notes in Computer Science series. The history of successful SPIN workshops is evidence for the maturing of model checking technology, not only in the hardware domain, but increasingly also in the software area. While in earlier years algorithms and tool development around the SPIN model checker were the focus of this workshop series, for several years now the scope has been widened to include more general approaches to software model checking techniques and tools as well as applications. The SPIN workshop has become a forum for all practitioners and researchers interested in model checking based techniques for the validation and analysis of communication prools and software systems.