Software has become ubiquitous and essential in our daily lives. The security of software systems is so important that must be ensured by building better and more secure software first. But software systems are becoming much more complex that make the software security engineering task very challenging. Model-Driven Security (MDS) promotes the notion of security by design and the use of models for engineering software systems at a high-level of abstraction and productivity. This book first reveals and analyses the current state of the art of MDS research. Then, it describes a full MDS framework focusing on modularity and reusability (called MDS-MoRe), which could be the basis for a complete MDS development lifecycle of secure systems. More precisely, MDS-MoRe is composed of a modular approach to deal with a specific but complex security concern, i.e. delegation in access control management. In fact, modularity enables adaptive system and security policy to coevolve at runtime. On the other hand, MDS-MoRe presents another approach promoting not only modularity but also reusability based on a System of Security design Patterns for addressing multiple security concerns systematically.