The present volume contains a selection of papers presented at the Seventh Workshop on Membrane Computing, WMC7, which took place in Leiden, The Netherlands, during July 17-21, 2006. The ?rst three workshops on membrane computing were organized in Curtea de Arge, s, Romania - they took place in August 2000 (with the proceedings published in Lecture Notes in Computer Science, volume2235), in August 2001(with a selection of papers published asa special issue of Fundamenta Informaticae, volume 49, numbers 1-3, 2002), and in August 2002 (with the proceedings published in Lecture Notes in Computer...