The message passing paradigmis the most frequently used approachto devel- ing high performance computing applications on parallel and distributed c- puting architectures.The ParallelVirtual Machine (PVM) and Message Passing Interface (MPI) are the two main representatives in this domain. This volume comprises 61 selected contributions presented at the 12th European PVM/MPI Users' Group Meeting, which was held in Sorrento, Italy, September 18-21, 2005. The conference was organized by the Dipartimento di Ingegneria dell'Informazione of the Second University of Naples, Italy in coll- oration with CREATE and the Institute of Graphics and Parallel Processing (GUP) of the Johannes Kepler University Linz, Austria. The conference was previously held in Budapest, Hungary (2004), Venice, Italy (2003), Linz, Austria (2002), Santorini, Greece (2001), Balatonfur .. ed, Hungary (2000), Barcelona, Spain (1999), Liverpool, UK (1998), and Krakow, Poland (1997). The ?rst three conferences were devoted to PVM and were held in Munich, Germany (1996), Lyon, France (1995), and Rome, Italy (1994). In its twelfth year, this conference is well established as the forum for users and developers of PVM, MPI, and other message passing environments. Int- actions between these groups have proved to be very useful for developing new ideas in parallel computing, and for applying some of those already existent to new practical ?elds. The main topics of the meeting were evaluation and p- formance of PVM and MPI, extensions, implementations and improvements of PVMandMPI,parallelalgorithmsusing the messagepassingparadigm,parallel applications in science and engineering, and cluster and grid computing.