At the tail end of his monumental trip of exploration and scientific discovery through Latin America from 1799 to 1804, the German naturalist Alexander von Humboldt visited President Thomas Jefferson in Washington. United by their common interests in the Enlightenment, they began a correspondence that endured until 1825. This contribution discusses a letter of 1811 by Humboldt to the former president, hitherto unpublished in English. Aside from closing a gap in their correspondence, the letter, although short, offers an illuminating insight into Humboldt’s personal, political, and scientific networks, which included such figures as Abbé José Correia da Serra and Joel Barlow, who were involved in his simple request for tobacco and seeds.