The concept of national security is essentially characterized by the malleability of its content, which is reflected by contrasting definitions that structure this area of studies. This article will try to point out the conceptual uncertainty which underlies our methodological problems. It includes the semantic questionability which is at the heart of its project, defines the scope of the concept of national security and states its conditions. Gathered, these considerations allow, through an analytical method, to reconcile the following triad : ontology - what is national security made of ? -, epistemology - how do we study it ? -, and politics - which are the variables that affect its implementation?.