In the world (but not yet in Russia specifically) there is already an extensive and rapidly growing amount of literature on the role and place of emotions both in international relations (IR) and in the foreign policy of states. This gives grounds to talk about the “emotional turn” within the framework of IR as a research discipline. But it is also well known that emotions are studied not only by IR, but in psychology, in various areas of neuroscience and in sociology as well. This article deals with some ontological and epistemological issues, arising from the results of multidirectional efforts of many academics to conceptualize the international political role of emotions on the basis of the leading international relations theories. The immediate goal is the exploration in the chosen subject area of the methodological problem of the integration of social science knowledge with achievements from the field of natural sciences. It is proposed to pay particularly close attention in this sense to the paradigm of affective neuroscience. The phenomenon of emotion, in principle, does not fit well with categories, which until now the IR has been focused on. Methodological imperatives of objective research push for the exclusion of subjective emotional experience from the scope of consideration. Constructivists, in their turn, treat emotion as a cognitive belief rather than as a bodily state. But in the article, the emotion is represented as a phenomenon which is both mental and physical. This is a monist view, going back to Spinoza. The research leads to the conclusion that, although social constructivism has good potential for studying the emotions in IR, when intentionally ignoring the biological nature of emotions, social constructivists can weaken their own position in comparison with those academic opponents, who are committed to instrumental rationalism in their approach. Constructivists thus limit with no good reason their own agenda when studying emotions and hinder the development of a transdisciplinary approach to the study of emotions in IR in particular.