This book introduces the Cognitive Early Warning Predictive System (CEWPS(TM)) as the new digital immune system. Similar to the human immune system, CEWPS relies on true or "inoculated" sickness experience to defend the body. The book also introduces The Smart Vaccine(TM), an intelligent agent that manages all the vaccination-as-a-service on the cloud before an attack happens. The book illustrates the current landscape of cyber warfare, highlights the vulnerabilities of critical infrastructure, and identifies the shortcomings of AVT. Next, it describes the concept, the architecture, and the enabling technologies required to build a digital immune system.