The Cybersecurity Dynamics framework offers an approach to systematically understanding, characterizing, quantifying and managing cybersecurity from a holistic perspective. The framework looks into cyberspace through the dynamics lens because environments in cyberspace often evolve with time (e.g., software vulnerabilities, attack capabilities, defense capabilities, and cybersecurity states). The dynamics lens offers a unique viewpoint, which guides the modeling of the various situations which evolve with respect to cybersecurity. This type of evolution is driven by attackers, defenders, and users of related systems and is manifested by their attack/defense/use activities. Since its inception in 2014, there has been significant progress in characterizing and taming various kinds of cybersecurity dynamics. In this paper we discuss the landscape and way-of-thinking that guide the Cybersecurity Dynamics model, including two killer applications and the technical barriers that serve as outstanding open problems for future research.