quality:correction
Spanish royal authorization, 1799

In Madrid, Humboldt sought authorization to travel to Spain's realms in the Americas; he was aided in obtaining it by the German representative of Saxony at the royal Bourbon court. Baron Forell had an interest in mineralogy and science endeavors and was inclined to help Humboldt. At that time, the Bourbon Reforms sought to reform administration of the realms and revitalize their economies. At the same time, the Spanish Enlightenment was in florescence. For Humboldt "the confluent effect of the Bourbon revolution in government and the Spanish Enlightenment had created ideal conditions for his venture".

The Bourbon monarchy had already authorized and funded expeditions, with the Botanical Expedition to the Viceroyalty of Peru to Chile and Peru (1777–88), New Granada (1783–1816), New Spain (Mexico) (1787–1803), and the Malaspina Expedition (1789–94). These were lengthy, state-sponsored enterprises to gather information about plants and animals from the Spanish realms, assess economic possibilities, and provide plants and seeds for the Royal Botanical Garden in Madrid (founded 1755). These expeditions took naturalists and artists, who created visual images as well as careful written observations as well as collecting seeds and plants themselves. Crown officials as early as 1779 issued and systematically distributed Instructions concerning the most secure and economic means to transport live plants by land and sea from the most distant countries, with illustrations, including one for the crates to transport seeds and plants.

When Humboldt requested authorization from the crown to travel to Spanish America, most importantly, with his own financing, it was given positive response. Spain under the Habsburg monarchy had guarded its realms against foreigner travelers and intruders. The Bourbon monarch was open to Humboldt's proposal. Spanish Foreign Minister Don Mariano Luis de Urquijo received the formal proposal and Humboldt was presented to the monarch in March 1799. Humboldt was granted access to crown officials and written documentation on Spain's empire. With Humboldt's experience working for the absolutist Prussian monarchy as a government mining official, Humboldt had both the academic training and experience of working well within a bureaucratic structure.

Before leaving Madrid in 1799, Humboldt and Bonpland visited the Natural History Museum, which held results of Martín Sessé y Lacasta and José Mariano Mociño 's botanical expedition to New Spain. Humboldt and Bonpland met Hipólito Ruiz López and José Antonio Pavón y Jiménez of the royal expedition to Peru and Chile in person in Madrid and examined their botanical collections.