This article focuses on the relevance of Alexander von Humboldt's correspondence in the formation of transatlantic scientific networks at the beginning of the nineteenth century. Apart from connecting Humboldt with scientists and scholars worldwide, his correspondence turned out to be a fundamental tool for assuring the material conditions and the social and scientific connections he needed to carry out his research on the Spanish colonies and to simultaneously diffuse his achievements on the European side of the Atlantic. His contact with Hispanic American scientists and with the local elites enabled him to build a broad social network, gaining access to key material, human and intellectual resources. The letters sent to scientists, scientific institutions and noblemen in Europe, for their part, kept Humboldt's European correspondents informed about his activities in Hispanic America, contributing to the validation of his work before the scientific community and the fulfilment of the duties resulting from the political and institutional support he received both before and during his travels. This stresses the importance of strategic social groups and their cooperation in the framework of exploratory travels as a means to gaining access to resources in the peripheries. It also reveals the scientist's dependence on all those who supported his research: kings, barons, botanical gardens, universities, and academies.
