The national security paradigm is a comprehensive framework or methodology that relates variables to one another and allows for diverse interpretations of American foreign policy in particular periods and contexts. National security policy encompasses the decisions and actions deemed imperative to protect domestic core values from external threats. This definition underscores the relationship of the international environment to the internal situation in the United States and accentuates the importance of people’s ideas and perceptions in constructing the nature of external dangers as well as the meaning of national identity, American ideals, and vital interests. This chapter outlines the key tasks to employ a national security methodology, beginning with identifying the key decision-makers, for example by reading memoirs, diaries, biographies, and oral histories. It then discusses the sources to use to appraise how these decision-makers assessed the intentions and capabilities of prospective foes, as well as perceptions of their own country’s strength and cohesion, the lessons of the past, the impact of technological innovations, and the structural patterns of the international system. The chapter emphasizes the importance of using empathy, understanding the core values of the past, and defining the meaning of power.