Research in software composition investigates models and techniques to build systems from predefined, pretested, reusable components instead of building them from scratch. In recent years, this idea has largely been adopted by - dustry. In the shape of service-oriented architecture, software composition has becomeaninfluentialdesignparadigm,especiallyforthe (re-)organizationof the IT infrastructure of organizations.On the technical level, the standardization of Web services and other composition technologies has further matured. Current research in software composition aims at (further) developing c- position models and techniques. The aspect-oriented programming and design paradigm, for instance, has gained interest in the research community as a c- position (support) model. Other current research questions concern the sp- ification of component contracts, in particular making explicit its observable behavior, and methods of correct components composition. The International Symposium on Software Composition provides a premier forum for discussing these kinds of research questions and presenting original research results. This LNCS volume contains the proceedings of the 5th International S- posium on Software Composition, which was held as a satellite event of the European Joint Conferences on Theory and Practice of Software (ETAPS) in Vienna, Austria, March, 25-26 2006. The symposium started with a keynote on “Semantically Enabled Service-Oriented Architectures” given by Dieter Fensel, Directorof theDigitalResearchInstitute.Themainprogramconsistedofpres- tations of research papers on software compositions. These proceedings contain the revised versions of the papers presented at SC 2006.