Even though Alexander von Humboldt spent only a short time exploring South and Central America (1799-1803) and his visit to the United States was rather short (roughly six weeks), Humboldt’s impact on American environmental history is as strong as that of many nineteenth-century politicians. He also has as many features named for him as some of those early leaders: Humboldt State University, Humboldt County, Humboldt Peak, and Humboldt River, to name a few. This is because his major five-volume work, Cosmos: A Sketch of a Physical Description of the Universe, had a direct effect on most of the scientific practitioners of the late nineteenth and early twentieth centuries. Useful resources include Nicolaas Rupke’s biography, Alexander von Humboldt: A Metabiography; Laura Dassow Walls’s The Passage to Cosmos: Alexander von Humboldt and the Shaping of America, which discusses the importance of Humboldt’s massive work; and Aaron Sachs’s The Humboldt Current: Nineteenth-Century Exploration and the Roots of American Environmentalism, which covers some of the same topics as The Passage to Cosmos.