As a species, we spend a great deal of time, energy, and money on security. The world’s military budgets alone totalled more than $1.9 trillion U.S. dollars in 2020, an average of 6.0 percent of government spending and 2.0 percent of Gross Domestic Product.1 The United States accounts for more than a third of the total all by itself and spends upward of $70 billion on foreign and military intelligence (a figure that excludes black budget expenditures).2 Add in spending on border controls, coast guards, and funding for national security–related research and development across a variety of fields, and it is clear that many countries invest very heavily indeed in protecting against foreign threats.

Before we can explore the ontology of security, we must establish a preferred meaning of the word and purge it, as far as possible, of ambiguity. This preliminary task is especially important when one’s subject is a term in common currency and deployed in a wide variety of contexts for a wide variety of purposes.1 The more familiar a word, the more likely we are to take for granted that our own particular understanding of it is widely shared and that its meaning goes without saying. This is as true of the word ‘security’ as it is for almost every other key concept in the study of world politics.