In this book, Arthur C. Mathieson and Clinton J. Dawes offer a complete and current treatment of the seaweeds of the Northwest Atlantic, including taxonomic descriptions, keys, and 108 plates of detailed line drawings of this rich assemblage of marine algal species found between the Canadian Arctic and Maryland. It is designed to serve as an up-to-date reference work, classroom text, and field manual for botanists, marine biologists, naturalists, and students learning about the highly diverse marine algal flora of the Northwest Atlantic Ocean. The introductory chapter provides a historical review of seaweed studies as well as a description of 15 geographical sites designated in the text. Three chapters on the green, brown, and red alga include more than 256 genera, 510 species, 10 subspecies, 21 varieties, and 14 forms. New taxonomic combinations and descriptions of several previously undescribed taxa are also included in the text. The modern classification reviews molecular as well as reproductive, morphological, and biological data. The work represents more than forty years of research on Northwest Atlantic seaweeds and will aid researchers throughout the Northeast and Southwest Atlantic coasts. The authors detail the taxonomy, morphology, cytology, and name derivation of various taxonomic entities, as well as the ecology and distribution patterns of over 555 taxa. The text includes keys to genera and species, a glossary, and sources of further information.