Complexity science is an interdisciplinary scientific field that analyzes systems as holistic entities consisting of characteristics beyond the sum of a system’s individual elements. This paper presents current research across the literature promoting cyber security as a complex adaptive system. We introduce complex systems concepts and fields of study, and deliver historical context, main themes, and current research relevant to cyber operations. Examples of cyber operations research leveraging agent-based modeling demonstrate the power of computational modeling grounded in complex systems principles. We discuss cyber operations as a scientific field, define current shortfalls for scientific rigor, and provide examples of how a complexity science foundation can further research and practice across a variety of cyber-based efforts. We propose standard definitions applicable to complex systems for cyber professionals and conclude with recommendations for future cyber operations research.