The present paper is the first part of the treatment of the Polychaeta collected by the Lund University Chile Expedition in 1948- 49; it only comprises the Errantia. No other collections are included in this treatment, but in order to give as complete a survey as possible of the Chilean polychaete-fauna and the distribution of each species along the enormous Chilean coast, the synopsis includes the species which - in the rather rich literature dealing with this subject - are reported from Chile. - Such species, which only come from literary "finds", are printed in brevier, and their finding places are given under the heading: Habitat. In the synopsis is only mentioned the synonymy of the species as far as the Chilean records up till now are concerned.