International relations theory is the study of international relations (IR) from a theoretical perspective. It seeks to explain causal and constitutive effects in international politics. Ole Holsti describes international relations theories as acting like pairs of coloured sunglasses that allow the wearer to see only salient events relevant to the theory; e.g., an adherent of realism may completely disregard an event that a constructivist might pounce upon as crucial, and vice versa. The three most prominent theories are realism, liberalism and constructivism.
