Field studies carried out between 1962 and 1968 along the Atlantic coast of Delaware, U.S.A., and the southern shores of Delaware Bay, revealed the presence of 74 different taxa of marine algae, 69 of which are benthic. Of these benthic taxa 11 belong to the Cyanophycophyta, 21 to the Chlorophycophyta, 1 to the Xanthophycophyta, 18 to the Phaeophycophyta, and 18 to the Rhodophycophyta. As reported in my Preliminary Checklists (Zaneveld, 1966a, 1967), almost all benthic taxa are new records for the State of Delaware, e.g. 11 belonging to the Cyanophycophyta, 18 to the Chlorophycophyta, 1 to the Xanthophycophyta, 16 to the Phaeophycophyta and 11 to the Rhodophycophyta. The reproductive periodicities of the taxa are tabulated, showing that the maximum reproductive periods for most taxa extend from early May to late September. The occurrence is seasonal in character; none of the taxa was found to occur all year round. The algal population was densest in the months of June, July, and August. With regard to the geographical distribution, all taxa are also reported to occur north of the Delaware Bay; 4 taxa of the Chlorophycophyta, 6 taxa of the Phaeophycophyta, and 1 taxon of the Rhodophycophyta, and none of the taxa of the Cyanophycophyta and the Xanthophycophyta seem to reach their southern limit along the coast of Delaware. Hence, the marine benthic algal flora of Delaware is temperate-boreal in character. The environmental factors checked indicate that inside the Delaware Bay, the temperature varies between −2 C and +30 C, and the salinity between 20.0‰ and 33.2‰. The structure of the bottom of the various collecting sites is mainly sandy along the Delaware Atlantic coast, and sandy-muddy inside the Delaware Bay.