Abstract Cybersecurity Dynamics is new concept that aims to achieve the modeling, analysis, quantification, and management of cybersecurity from a holistic perspective, rather than from a building-blocks perspective. It is centered at modeling and analyzing the attack-defense interactions in cyberspace, which cause a “natural” phenomenon— the evolution of the global cybersecurity state. In this Chapter, we systematically introduce and review the Cybersecurity Dynamics foundation for the Science of Cybersecurity. We review the core concepts, technical approaches, research axes, and results that have been obtained in this endeavor. We outline a research roadmap towards the ultimate research goal, including a systematic set of technical barriers.