A synopsis is presented of the Neotropical orchid genus Xylobium, wherein 18 species are recognized, including one new species and three varieties. A key is supplied to help identify the species, along with discussion under each entity on its recognition characters, notes where necessary on the synonymy, and a list of specimens examined. The new names are X. miliaceum var. patens, X. undulatum var. portillae, X. undulatum var. variegatum, and X. wilhelminae. At the end of the treatment, a list of excluded taxa is provided, which includes the currently known status of each name. Among those taxa, Dendrobium longifolium is neotypified, and the combinations Cyrtochilum bicolor and Sudamerlycaste insolita are proposed.