Rhinoceros sondaicus Desmarest, 1822, commonly called the Javan rhinoceros or lesser one-horned rhinoceros, is the most critically endangered large mammal on Earth with only 40–50 extant individuals in 2 disjunct and distant populations: most in Ujung Kulon, West Java, and only 2–6 (optimistically) in Cat Loc, Vietnam. R. sondaicus is polytypic with 3 recognized subspecies: R. s. sondaicus (currently West Java), R. s. inermis (formerly Sunderbunds; no doubt extinct), and R. s. annamiticus (Vietnam; perhaps now extinct). R. sondaicus is a browser and currently occupies lowland semievergreen secondary forests in Java and marginal habitat in Vietnam; it was once more widespread and abundant, likely using a greater variety of habitats. R. sondaicus has a very spotty history of husbandry, and no individuals are currently in captivity. Conservation focuses on protection from poaching and habitat loss. Following decades-long discussion of captive breeding and establishment of a 3rd wild population, conservation and governmental agencies appear closer to taking such seriously needed action on the latter.