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 ?rst 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...