The worldwide operations of the Department of Defense (DoD) inevitably include dependence upon both domestic and foreign sources of raw materials, equipment, inputs, components, technology and associated expertise, and other important goods. This report develops and illustrates a method for analyzing "vulnerabilities" purportedly yielded by foreign and domestic dependencies. It discusses the nature of "insurance" in this context and examines the distinction between "dependence" and "vulnerability." The authors identify signs of potential vulnerability for which the DoD should be alert. Under some conditions, ironically, domestic dependencies yield greater vulnerability than foreign ones. They then examine four dependence examples — tritium, surface acoustic wave technology, dynamic random access memory chips, and high-density television — as a means of illustrating the method they developed and of gaining insights into the critical relationships.