Many of the words used to describe disease ('infection', 'transmission', 'virus') are also used to characterize cyber security (for example: a computer is infected by a virus that can be transmitted to other current uninfected computers). This correspondence is much more than a convenient metaphor, and the aim of this book is to show how the models developed to understand the dynamics of infection, recovery, and possible reinfection in disease can be applied to understand attack, compromise, and recovery of components of a cyber system and how such attacks affect performance of the cyber system or its dependent enabled physical system.