Since the appearance of the first documentation of marine algae from within the political boundaries of eastern Canada (South & Cardinal, 1970), a sufficiently large volume of new information has become available to warrant the revision presented here. Taxonomic and systematic changes, together with further additions, corrections and emendations are incorporated as far as possible. A total of 346 species, subspecies and varieties are listed, comprising 131 Rhodophyta, 127 Phaeophyta and 88 Chlorophyta. The treatment is largely restricted to macroscopic forms. Inclusion of microscopic species of Chlorophyta and representatives of other marine Phyla is planned for the future.