Horsfeld's tarsier is the only species of tarsier in the genus Cephalopachus. Named by American naturalist Thomas Horsfield, it is also referred to as western tarsier. The species occurs on Borneo, Sumatra and nearby islands and is, like other members of the group, entirely nocturnal.

Tarsiers are haplorhine primates of the family Tarsiidae, which is, itself, the lone extant family within the infraorder Tarsiiformes. Although the group was, prehistorically, more globally widespread, all of the species living today are restricted to Maritime Southeast Asia, predominantly being found in Brunei, Indonesia, Malaysia and the Philippines.