What ‘border security’ or ‘secure borders’ denote in the EU is not defined. The article explores the concept of border security and how the concept of border security found its way into the supranational EU legislation on border control. The core of the concept of border security can be seen as consisting of ‘border control’, referring to the maintaining of controls of individuals crossing the EU external borders. The developments towards the use of the term border security seemingly encompass, at least, the evolution of the EU internal security domain, a qualitative change in the nature of a number of border control related measures, the perception of insecurities related to the 2004 EU enlargement and the 11 September 2001 attacks. At least at the time when Frontex became operational in 2004, a border security rhetoric began to be used in the EU. Today, the term border security is well established in EU actors’ rhetoric. The supranational EU rules containing the term border security are fundamental elements of the EU border policies and play a crucial role in contributing to the EU discourse on border issues.