Since the beginning of civilization, every country has always been interested to know the defence system of the other countries and are making constant efforts to make a well-built and efficient defence system than the other nations. Thus, the size and the pattern of military expenditure of a country does not depend only on its GDP or financial capability; in addition it depends on various other factors. All these factors may be identified as economic, non-economic, internal, external, political, geographical, geopolitics and geostrategic factors among others. All these factors are playing a vital role in determining the size and the composition of the military expenditure of a country. Military Expenditure is the amount of financial resources allocated by a nation to maintain armed forces and other essential services for defence purpose. Military expenditures are one of the most critically observed components of public expenditure. The standard definitions of military expenditure have been proposed by some international organizations and research institutes that are involved in the study of the defence sector. In this issue, one of the vital problems is how to define military expenditure or which public expenditure should be a part of military expenditure, further what are the main determinants of the military expenditure of a country.