This book constitutes the thoroughly refereed extended postproceedings of the 9th International Workshop on Membrane Computing, WMC 2008, held in Edinburgh, UK, in July 2008 under the auspices of the European Molecular Computing Consortium (EMCC) and the Molecular Computing Task Force of IEEE Computational Intelligence Society.

The 22 revised full papers presented together with 5 invited papers went through two rounds of reviewing and improvement. The papers in this volume cover all the main directions of research in membrane computing, ranging from theoretical topics in mathematics and computer science to application issues. A special attention was paid to the interaction of membrane computing with biology and computer science, focusing both on the biological roots of membrane computing, on applications of membrane computing in biology and medicine, and on possible electronically based implementations.