Abstract Until recently, a major gap has existed in our knowledge regarding Mexican bird information from the Real Expedición Botánica a Nueva España in the late 1700s. This expedition (1787–1803) was commanded by Martín de Sessé; the Mexican scientist José Mariano Mociño joined the group in 1790, but his ornithological findings were never published and have long been considered lost. However, study of the Sessé-Mociño ornithological results began in 1979 with the appearance of a small collection of original paintings, apparently from the expedition. Later, in 1997, unpublished manuscripts were discovered in the library of the Museo Nacional de Ciencias Naturales, Madrid that included descriptions of many bird species, again apparently Sessé-Mociño material. These discoveries, covering an important portion of the overall ornithological results of the expedition, make possible a broader study of the Sessé-Mociño ornithology: a taxonomic list using modern nomenclature, an analysis of the correspondence between the paintings and the manuscripts, and conclusions regarding the provenance of those materials. Of a total of 83 paintings available, we were able to identify 78 to species, and 5 only to family. In the manuscripts, 290 species were treated, but for 27, the descriptions were fragmentary and insufficient for identification; of the remaining 263 species, we arrived at a species-level identification for 242, and identified the remainder to genus (19) or family (2). The recent discovery of these ornithological texts and paintings offers a unique view of the history of ornithology as well as of the environmental history of Mexico.