With the increasing adoption of Model-Based Development in many domains (e.g., Automotive Software Engineering, Business Process Engineering), models are starting to become core artifacts of modern software engineering processes. By raising the level of abstraction and using concepts closer to the problem and application domain rather than the solution and technical domain, models become core assets and reusable intellectual property, being worth the effort of maintaining and evolving them. Therefore, increasingly models experience the same issues as traditional software artifacts, i.e., being subject to many kinds of changes, which range from rapidly evolving platforms to the evolution of the functionalities provided by the applications developed. These modifications include changes at all levels, from requirements through architecture and design, to executable models, documentation and test suites. They typically affect various kinds of models including data models, behavioral models, domain models, source code models, goal models, etc. Coping with and managing the changes that accompany the evolution of software assets is therefore an essential aspect of Software Engineering as a discipline.