The end of World War II marks the beginning of a major debate on the questions of epistemology and ontology in Security Studies. It began with the objectivity-materialism approach, also known as traditional approach pioneered by neo (realism) and (neo) liberalism. This approach that dominates the Cold War era attempted to understand the issue of security by using the systematic approach. This perspective believes that all social phenomena including security issues can only be understood by using a scientific approach, namely science. This perspective later evolved and became one of the most dominant approaches in Security Studies throughout the Cold War period. However, in the 1980s and 1990s, this traditional approach was challenged by several other approaches that purport to study security issues from a different perspective. This scenario, in turn, led to the emergence of the subjectivity-ideational and discursive perspectives which seek to understand security from different epistemology and ontology point of view. For that purpose, this article discusses the evolution of Security Studies, from the objectivity-materialism that dominates the debate of security during the Cold War (also known as traditional); to the emergence of subjectivity-ideational through critical approach; and, as well as the discursive approach that emphasizes the role of language in understanding the security phenomenon. This article employs qualitative approach focusing on library research. It argues that these different ways of seeing security are particularly essential in explaining the increasingly complex international security phenomenon.