Software systems are changed continuously. For instance, in order to repair a reported bug or in order to ensure that a new functional requirement is met. This constant need for change drives the manner in which modern software systems are developed, as evidenced by the trend towards iterative and agile development processes. Automated testing approaches, bug trackers and static analyses still start from the fundamental assumption that they act upon a single, complete release of the system. As a result, there exists a remarkable disparity between the trend towards embracing change and the tools used by today's software engineers. The main objective of this project is to devise innovative tools that enable change-centric software development. This by representing changes themselves as first-class entities. Concretely, we will investigate how to safeguard a system's quality in an incremental manner, how to repeat changes reliably on a closely-related system, and how to maintain changes throughout a system's lifetime ---all by manipulating first-class changes.