Volume 11 of Résultats des Campagnes MUSORSTOM (which is volume 158 in the parent series Mémoires du Muséum National d'Histoire Naturelle) reports on the benthic deep-sea fauna from the tropical Western Pacific, with emphasis on the New Caledonian region. The seven contributed papers cover the taxonomy and biogeography of selected groups of invertebrates (one paper each on sponges, hydroids, bryozoans, pycnogonids and ascidians) and fishes (two papers). Of the 209 species studied, as many as 116, plus 3 subspecies, are described as new, thus demonstrating once again the richness and outstanding peculiarity of the fauna inhabiting the slopes of New Caledonia. This includes a remarkable radiation of 20 new species in a new genus of Sertulariidae (Hydrozoa) and more species of Petalostegidae and Bifaxariidae (Bryozoa) than anywhere else in the world. In addition, there are numerous new records and range extensions. The MUSORSTOM series is a joint program of the Muséum national d’Histoire naturelle and the Institut Français de Recherche Scientifique pour le Développement en Coopération (ORSTOM).