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 re-infection 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.