This volume originated in the Workshop on Membrane Computing, WMC- CdeA 2002, which took place in Curtea de Arge, s, Romania, during August 19- 23, 2002.This was the third annual workshop held in Curtea de Arge,s.The ?rst one, Workshop on Multiset Processing, WMP-CdeA 2000, took place in August 2000, and the proceedings were published in Lecture Notes in Computer Science, volume 2235.The second one, Workshop on Membrane Comp- ing, WMC-CdeA 2001, took place in August 2001, and selected papers were published as a special issue of Fundamenta Informaticae, volume 49, numbers 1-3, 2002. The aim of these workshops is to provide a stimulating environment for - searchers working in the area covered by a given workshop, so that existing sci- ti?c collaborations can be strengthened, and new collaborations (and friendships) can be initiated.Indeed, all three workshops held up to now were of such ch- acter, with very international attendance and collaboration taking place across national and scienti?c boundaries.