In this paper, we first demonstrate the historical background for the current unsatisfactory state of systematics of the polychaetes. We then briefly discuss our knowledge of internal and external structures. A review of the polychaete families makes up the third section; 81 families are treated in detail. Five families have been recently synonymized with others, and six families are too poorly known to be sufficiently characterized. Fossil polychaetes are briefly mentioned, with specific attention to problems associated with incorporating them in recent systematics.

The traditional separation in ‘errant’ and ‘sedentary’ polychaetes has increasingly become recognized as being unsatisfactory; however, the current trend towards grouping the polychaetes in many orders without specifying the relationships among the orders, is no more satisfactory. The lack of consistent morphological information is a major source of uncertainty. Intensive morphological studies should remove terminological ambiguities and alleviate some of the problems.