Transnational historiography, which emerged in the 1990s, covers historical phenomena that transcend the boundaries of the nation-state, analyzing the processes of circulation, transformation and hybridization of scientific ideas and practices across national frontiers. When scientific knowledge flows between different countries, the ideas that emerge in one particular national context adapt to the new local contexts of their hosts, with their particular cultural, social, political and scientific traditions. In psychology, the transnational approach provides a productive theoretical framework capable of going beyond the traditional US-centered perspective that has dominated the historiography of psychology since the mid-20th century. This US-based historiography has, for example, interpreted the historical influence of I. P. Pavlov in terms of two main factors: his methodological contribution—the conditioned reflex—and the existence of a behaviorist tradition in the receptor psychology community. However, a more global analysis questions the need for these two elements and, at the same time, offers insights into the conditions that facilitated or hindered the flow of Pavlovian science beyond the United States. Thus, for example, between 1903 and 1970 the dissemination and appropriation of the Pavlovian science of conditioned reflexes took two different routes: in America, scientific aspects and factors dominated; whereas elsewhere, politics prevailed over science. This happened in countries such as China, Cuba, and Spain, with dictatorial regimes at different ends of the political spectrum, where Pavlov’s work arrived under the auspices of government programs to modernize scientific and clinical institutions. Once Pavlov’s ideas had been introduced through reform programs in each country, they were accepted or rejected depending on whether the sign of the regime in question converged with the ideology prevailing in the Soviet Union, which it did in China and Cuba, but not in Spain. In these countries, where psychology did not have strong institutional roots and behaviorism was not a dominant approach, Pavlovian ideas found a receptive audience among health professionals-doctors, psychiatrists, and clinical psychologists - keen to embrace new ideas and treatments for mental disorders. Thus, from a transnational perspective, the global repercussion of Pavlov’s ideas went far beyond the strictly methodological sphere.