The evolution in software development methods during the last decade, towards short iterations and frequent feedback, also come with new challenges, especially when considering critical systems where incorrect behavior can cause harm to people or to the environment as well as substantial economic loss. As critical functionalities are increasingly handled by software, there is on one hand a need to systematically assess that the system is acceptably safe, and on the other hand to be able to respond quickly to new needs or when new security vulnerabilities are discovered. The research in this theme addresses challenges that arise when balancing the need for architectural quality and more agile ways of working, with shorter development cycles. For example: How do we work effectively with other evolving artifacts than code, including models and documentation? How can safety and security assurance be done more incrementally and allowing for reuse of information between product variants?