The present paper is a systematic geographical treatment of the Polychaetes from the north-western parts of the Atlantic Ocean, north of the 60° N. Lat. and West of 0° Long. The collections mainly originate from the Danish cruiser "Ingolf" which, in the summers of 1895 and 1896 made two scientific deep-sea expeditions of four months each in the seas round the Faroes, Iceland and Greenland. Though more than 50 years have elapsed since the "Ingolf" brought home her collections, the comprehensive material is still of considerable value, mainly because no new collections of importance have been made in the abyssal regions of the North Atlantic. Nevertheless, the collections of the Zoological Museum proved to comprise some material from the area under consideration, and it seemed natural to include into this treatment these small and more accidental collections from other expeditions; thus the Polychaetes collected, e.g. by the "Thor", the "Dana", the "Tjalfe" and the "Michael Sars", and by Danish officials in Greenland have been treated here too.