The known terrestrial vertebrate fauna of the New Hebrides consists of 16 species of mammals (excluding feral domestic stock), 61 species of resident land- and fresh-water birds, 20 species of reptiles and one amphibian. Of these, three, five, four and one species respectively have apparently been introduced by man. The non-introduced fauna is clearly Indo-Australian in origin, but some species have an exclusively Pacific island distribution and others (two bats, seven birds, and four lizards) are endemic. On the six islands visited 95 out of the possible 98 vertebrate species occur. Santo, the largest and most northerly island, supports the richest fauna. The comparative impoverishment of more southerly islands is not directly attributable to the progressive increase in isolation and distance from presumptive source area, nor to decrease in island area or maximum height. Most of the native vertebrates, including all endemic species, occur in mature seral or climax forest; relatively few species, all of which are cosmopolitan or wide-ranging in the Indo-Pacific region, are restricted to open habitats. Of introduced vertebrates only the feral pig, Rattus exulans and Gallus gallus occur in forest; the remainder are commensal with man or confined to disturbed or open habitats. Forest faunas show altitudinal zonation and vertical stratification under the canopy. The ranges of three large skinks are mutually exclusive, and may be complementary. No bats or birds have comparable complementary distributions, but among four closely related pairs of birds the niche of species widespread in the archipelago is reduced in the presence of a less widely distributed relative. The diversity of the netted avifauna was constant despite marked variation in the diversity of canopy trees in the netting plots. Vegetational characteristics also failed to correlate with the presence or absence of bird species irregularly distributed throughout the archipelago. There have been suggestions that some forest-adapted species (pigeons, lorikeets) may move from island to island but direct observations are lacking. Among Halcyon chloris and many passerines interrupted distributions, differences in habitat preference and/or taxonomically significant differences in size or colour indicate limited exchange between adjacent islands, implying that populations are sedentary. The distribution of certain bird species indicates that active colonization of the New Hebrides is not yet complete. Artamus leucorhynchus has apparently invaded Aneityum in recent years. The present distribution of Lichmera incana is also interpreted in terms of current invasion, and suggests that a preliminary period of selection is necessary before an invader can advance from the coastal strip into the forested interior.