Invited Lectures.- Investigation of a Biological Repair Scheme.- An Introduction to BioModel Engineering, Illustrated for Signal Transduction Pathways.- Multilevel Modeling of Morphogenesis.- A Definition of Cellular Interface Problems.- A Multiscale Modeling Framework Based on P Systems.- Regular Papers.- On the Qualitative Analysis of Conformon P Systems.- Dual P Systems.- Solving PP-Complete and #P-Complete Problems by P Systems with Active Membranes.- Fast Synchronization in P Systems.- Membrane Systems Using Noncooperative Rules with Unconditional Halting.- Modeling Ecosystems Using P Systems: The Bearded Vulture, a Case Study.- MetaPlab: A Computational Framework for Metabolic P Systems.- Usefulness States in New P System Communication Architectures.- A P-Lingua Programming Environment for Membrane Computing.- On Testing P Systems.- Hebbian Learning from Spiking Neural P Systems View.- Event-Driven Metamorphoses of P Systems.- Effects of HIV-1 Proteins on the Fas-Mediated Apoptotic Signaling Cascade: A Computational Study of Latent CD4+ T Cell Activation.- Transforming State-Based Models to P Systems Models in Practice.- How Redundant Is Your Universal Computation Device?.- Enumerating Membrane Structures.- Toward an MP Model of Non-Photochemical Quenching.- Applications of Page Ranking in P Systems.- An Algorithm for Non-deterministic Object Distribution in P Systems and Its Implementation in Hardware.- First Steps Towards a Wet Implementation for ?-DPP.- Defining and Executing P Systems with Structured Data in K.- Translating Multiset Tree Automata into P Systems.

This volume contains a selection of papers presented at the 9th Workshop on Membrane Computing, WMC9, which took place in Edinburgh, UK, during July 28-31,2008. The ?rst three workshopson membrane computing were or- nized in Curtea de Arge¸ s, Romania - they took place in August 2000 (with the proceedings published in Lecture Notes in Computer Science, volume 2235), in August 2001 (with a selection of papers published as a special issue of Fun- menta Informaticae, volume 49, numbers 1-3, 2002), and in August 2002 (with the proceedings published in Lecture Notes in Computer Science, volume 2597). The next ?ve workshops were organized in Tarragona, Spain, in July 2003, in Milan, Italy, in June 2004, in Vienna, Austria, in July 2005, in Leiden, The Netherlands, in July 2006, and in Thessaloniki, Greece, in June 2007, with the proceedings published as volumes 2933, 3365, 3850, 4361, and 4860 of Lecture Notes in Computer Science.