Resilience is a relatively new conceptual category used when considering security and defence. It means adaptability, resistance to threats, flexibility of response, and the ability to regenerate. The term resilience has been present in English for a long time, as evidenced by the presence of this term in old dictionaries of the English language. Originally, its meaning related to medicine and mechanics, a bit later – to human psychology, and today it has extended to the issues of resilience of cities, societies, and entire countries. An attempt at applying this new conceptualisation is associated with the recognition that the current security paradigm is losing its relevance in a rapidly changing and complex world. The changing scale of threats makes it necessary to search for new theoretical foundations for creating an effective defence policy. However, the theory of resilience has not yet been fully formulated, at best, only its theorem has. The aim of this article is to present the significance of this conceptual category, to indicate the theoretical concepts underlying this conceptualisation in social sciences, and to reflect on the value of the concept of resilience for security and defence.