Any system that has many parts, pieces, elements, or agents that can choose and interact dynamically in nonlinear fashions would be considered as Complex Adaptive. These systems show the spontaneous formation of distinctive temporal, spatial, or functional structures. They evolve through time, are dynamic, and can change their internal and external interactions or structures. Complex Adaptive Systems offer macro and holistic mental models to resolve challenging issues such as international socio-political tensions, urban development growth, the electric grids, global internet networks, economic and technological dynamics, to name a few. In this book, we plan to explain introductory concepts and more qualitative aspects of what Complex Adaptive Systems are, and why we need to understand them.