This book constitutes the refereed proceedings of the 9th International Conference on Model Driven Engineering Languages and Systems (formerly the UML series of conferences), MoDELS 2006, held in Genova, Italy, in October 2006. The 51 revised full papers and 2 invited papers presented were carefully reviewed and selected from 178 initial submissions. The papers are organized in topical sections on evaluating UML, MDA in software development, concrete syntax, applying UML to interaction and coordination, aspects, model integration, formal semantics of UML, security, model transformation tools and implementation, analyzing dynamic models, specifying transformations, MOF, bridging models, risk, trust and dependability, tool environments, OCL, roundtrip engineering, real time and embedded systems, as well as workshops, tutorials and panels.