Now available in a paperback edition, updated with 30 pages of additions and corrections, this work provides a systematic treatment of almost every group of marine invertebrates of the Pacific Northwest. Close to 4,000 species are covered and many are illustrated by photographs or drawings. Developed over a period of more than 30 years by zoologists associated with the Friday Harbor Laboratories of the University of Washington and several other institutions, the keys, taxonomic lists, and bibliographies are relevant tonvertebrates of intertidal and shallow subtidal habitats between southern Oregon and the Queen Charlotte Islands of British Columbia. This book is essential for students of invertebrate zoology, marine biology, marine ecology, and fisheries ecology.