The purpose of this paper is to introduce and evaluate regional-level theories in international security studies. The first part explains why region as analytical level has been neglected in conventional IR theories, particularly among realist scholars. It will be followed by discussions about how region is gradually recognized in the field of security studies as a new and supplementary level of analysis. The second half of the paper introduces two regional-level theories in security studies today: security communities and regional security complexes. The last part assesses influence of both theories as a way of understanding whether a regional-level theory is appropriate for future researches on international disputes or conflicts.