The method used to collect the data on which this book is based was derived from the work we undertook in Probabilistic Risk Identification, Mapping (to mitigation mechanisms that are currently in place), and Evaluation (PRIME). The general concepts developed as part of conducting this work are explained in this chapter. Because of the nature of the theme this chapter addresses, it is a little more theoretical than the rest of the book. The reader who wants get to the heart of the matter can read Chapter 16 without incurring any loss in ability to comprehend the assessment results.