Present anti-virus technologies do not have the symmetrical weaponry to defeat massive DDoS attacks on smart cities. Smart cities require a new set of holistic and AI-centric cognitive technology, such as autonomic components that replicate the human immune system, and a smart grid that connects all IoT devices. The book introduces Digital Immunity and covers the human immune system, massive distributed attacks (DDoS) and the future generations cyber attacks, the anatomy and critical success factors of smart city, Digital Immunity and the role of the Smart Grid, how Digital Immunity defends the smart city and annihilates massive malware, and Digital Immunity to combat global cyber terrorism.