Homeland security is a recognized practice, profession and field without a unifying theory to guide its study and application. The one previous attempt by Bellavita [2] acknowledges its own shortcomings and may be considered incomplete at best. The failure may be attributed to the lack of an underlying correlating factor. This chapter demonstrates that “domestic catastrophic destruction” is the correlating factor that unites key historical homeland security incidents and this observation is leveraged to propose a theory of homeland security that is descriptive, prescriptive and predictive. The proposed theory is descriptive because it can differentiate between what is and what is not homeland security. The theory is prescriptive because it can suggest an optimum homeland security strategy. It is predictive because it renders homeland security into a technical problem and demonstrates how its effects may eventually be blunted through the technological evolution and revolution of the critical infrastructure. Accordingly, the proposed theory embodies a set of foundational principles to guide the study and application of the practice, profession and field of homeland security.