This volume contains a selection of papers presented at the 10th Workshop on Membrane Computing, WMC 2009, which took place in Curtea de Arge, s, Romania, during August 24-27, 2009. The?rstthreeWorkshopsonMembraneComputingwereorganizedinCurtea de Arge, s, Romania - they took place in August 2000 (with the proceedings p- lished in Lecture Notes in Computer Science, volume 2235), in August 2001 (with a selection of papers published as a special issue ofFundamenta Inform- icae, volume 49, numbers 1-3, 2002), and in August 2002 (with the proceedings publishedinLectureNotesinComputerScience, volume2597).Thenextsixwo- shopswereorganizedinTarragona, Spain(inJuly2003), inMilan, Italy(inJune 2004), in Vienna, Austria (in July 2005), in Leiden, The Netherlands (in July 2006), in Thessaloniki, Greece (in June 2007), and in Edinburgh, UK (in July 2008), with the proceedings published as volumes 2933, 3365, 3850, 4361, 4860, and5391, respectively, ofSpringer'sLectureNotesinComputerScience. The workshop changed its name in 2010, and the series will continue as the Conference on Membrane Computing, with the next edition, CMC11, to be held in Jena, Germany. The tenth edition of WMC took place in Hotel Posada in Curtea de Arge, s (http: //www.posada.ro/)anditwasorganizedbytheNationalCollege"Vlaicu Voda" ? of Curtea de Arge, s, the University of Pite, sti, Romania, and the Institute of Mathematics of the Romanian Academy, Bucharest, under the auspices of the European Molecular Computing Consortium (EMCC) and IEEE Compu- tional Intelligence Society EmergentTechnologies Technical Committee Mole- lar Computing Task Force, with the ?nancial and organizational support of the Council of Arge, s County and Seville University."

This Festschrift is in honor of Mario de Jesus Perez-Jimenez, Professor in the Department of Computer Science of University of Seville, Spain, on the occasion of his 70th birthday. The title of this volume reflects both his main research area, viz., Natural Computing, and the guiding principle of his functioning: "once you choose to do something, enjoy doing it". The respect that Professor Mario de Jesus Perez-Jimenez enjoys in the scientific community was well demonstrated by the enthusiastic response received to the request to contribute to this book. The contributions by more than 70 authors from 15 countries cover a wide spectrum of research areas and reflect well the broad range of research interests of Professor Mario de Jesus Perez-Jimenez. The research areas presented in this Festschrift include membrane computing, spiking neural networks, phylogenetic networks, ant colonies optimization, workbench for biocomputing, reaction systems, entropy of computation, rewriting systems, and insertion-deletion systems.