In this article we propose a mode of analysis that allows us to consider security as a form distinct from insecurity, in order to capture the heterogeneity of security objects, logics and forms of action. We first develop a genealogy for the anthropology of security, demarcating four main approaches: violence and state terror; military, militarization, and militarism; para-state securitization; and what we submit as ‘security assemblages.’ Security assemblages move away from focusing on security formations per se, and how much violence or insecurity they yield, to identifying and studying security forms of action, whether or not they are part of the nation-state. As an approach to anthropological inquiry and theory, it is oriented toward capturing how these forms of action work and what types of security they produce. We illustrate security assemblages through our fieldwork on counterterrorism in the domains of law enforcement, biomedical research and federal-state counter-extremism, in each case arriving at a diagnosis of the form of action. The set of distinctions that we propose is intended as an aid to studying empirical situations, particularly of security, and, on another level, as a proposal for an approach to anthropology today. We do not expect that the distinctions that aid us will suffice in every circumstance. Rather, we submit that this work presents a set of specific insights about contemporary US security, and an example of a new approach to anthropological problems.