This book constitutes the refereed proceedings of the 8th International Symposium on Software Composition, SC 2009, held in Zurich, Switzerland, in July 2009. The workshop has been organized as an event co-located with the TOOLS Europe 2009 conference. The 10 revised full papers presented together with 2 invited lectures were carefully reviewed and selected from 34 submissions. The papers reflect current research in software composition to foster developing of composition models and techniques by using aspect- and service-oriented programming, specification of component contracts and protocols, methods of correct components composition, as well as verification, validation and testing techniques - even in pervasive computing environments and for the Web.