It is well established that intelligence testing in its modern form developed and was deployed slightly differently in several countries, most notably France, England and the United States. Less widely recognized is the fact that its originators were all part of a close network of scholars who liaised internationally, exchanged ideas and were thoroughly acquainted with each other's work. Their exchanges resulted from the transnational drive to develop a new social science of psychology involving a determination to find empirical evidence on which to base understandings of the human mind. This soon led to the development of a means of testing human performance, not least in the field of intelligence. In the process, close contacts between all those who were to be pioneers of intelligence testing around the globe developed, in touch with and feeding off each others' ideas. This article is an account of the development of that network.