The programming language dictates how developers can describe data structures, interfaces, and algorithms. The libraries provide an extensive array of advanced services to the program such as data access, communications, and graphical user interface. The language and libraries are called the platform. The platform sets the rules and makes the system possible. However, over the course of a system's lifespan, the platform can and will change: languages and libraries inevitably evolve and are replaced by next-generation technologies. Usually, the changes are gradual with an appropriate measure of backward compatibility, so we can adapt through standard maintenance activities. Sometimes, however, the changes are more radical and disruptive, so a more focused effort, called a migration project, is called for.