This chapter discusses the basic elements of an approach that will determine the type of physical security most appropriate for a particular electric system. The protection of the electric system now requires that an owner/operator use a systematic, comprehensive approach to the development and design of a physical substation security system. Many believe that the size of the system, the rate of growth, the lack of investment, the demand on reliability, and the changes in business structure make the system more vulnerable to failure than in the past. The group conducted a nationwide survey to collect data on the effectiveness of the most common security systems in use at the time. Regardless of intent, an owner/operator must choose the appropriate physical security methods to protect the substation from as many threats as possible. A comprehensive system analysis must take into account two important ideas: a substation’s “criticality” and a substation’s “vulnerability.”