“Human security” has occupied a significant place in the global discourses of peace, development, and diplomacy, despite often made criticisms of its conceptual ambiguity. Arguing for the merit of a broader definition of human security, i.e. “the right of people to live in freedom and dignity, free from poverty and despair” (UN Resolution A/RES/66/290), this paper offers an interdisciplinary theoretical framework in which key aspects of human security are systematically laid out: types of threats from physical, living, and social systems; causal structures that produce threats to human security; instruments to deal with these threats; and issues of agency to protect human security. The tripartite differentiation of the sources of threats -- physical, living, and social systems -- roughly corresponds with the objects of inquiry of three groups of academic disciplines: (1) sciences and engineering based on physics and chemistry, (2) biological and ecological sciences, and (3) social sciences and the humanities. This paper argues that a desirable theory of human security should rely on these multiple disciplines for the causal mechanisms that produce human security threats. It also contends that the theory should explore the interaction among different systems because threats to human security impact the physical, biological, and social aspects of human beings. In analyzing human security threats within the social system, this paper stresses the importance of analyzing the "collective action" aspects of human security threats. It argues, for example, the theoretical relevance of the Hobbesian "state of nature" as a condition where human security is chronically threatened socially. As to the types of measures to protect human security, this paper differentiates the instruments to affect the causes of the threat and those affecting the consequences. This paper argues that desirable instruments should be selected based on the analysis of the nature of the threat and its underlying causal mechanism. Finally, this paper discusses the issues of agency to protect human security: who should protect whose human security? Stressing the importance of responsible sovereign states as crucial agents to protect human security, this paper also argues that, given the global and interconnected nature of human security threats, cooperation among various stakeholders -- states, international organizations, the business sector, civil society organizations, academic institutions, and so on -- is essential.
