In the past, national security for the majority of countries was almost exclusively associated with an external military threat emanating from a rival state(s). This was reflected in the standard models for the demand for military expenditure. The emergence of new security challenges such as terrorism, transnational crime networks, failed and rogue states, has profoundly affected the international security environment and the concept of national security. This note develops a model for the demand for national security expenditure adopting a broader, more inclusive definition of national security and includes concomitant budgetary outlets to meet the new security challenges.