The benthic marine algal order Gigartinales (Rhodophyta) is introduced, and a key to the families found between Cross Sound, Alaska, and northern Washington is provided. The family Dumontiaceae is monographed. Ten of 16 currently recognized genera and 14 of some 48 recognized species are described and illustrated: Constantinea rosa-marina (Gmelin) Postels et Ruprecht, C. simplex Setchell, C. subulifera Setchell, Cryptosiphonia woodii (J. G. Agardh) J. G. Agardh, Dilsea California (J. G. Agardh) Kuntze, Dumontia contorta (Gmelin) Ruprecht, D. simplex Cotton, Farlowia mollis (Harvey et Bailey) Farlow et Setchell in Collins, Holden, et Setchell, Neodilsea borealis (Abbott) Lindstrom, N. natashae Lindstrom, Orculifilum denticulatum Lindstrom, Pikea californica Harvey, Thuretellopsis peggiana Kylin, and Weeksia coccinea (Harvey) Lindstrom. Farlowia compressa J. G. Agardh is recognized as a taxonomic synonym of F. mollis, and Pikea robusta Abbott as a taxonomic synonym of Pikea californica. Vegetative keys to the genera and species of the family are also included. Basionyms, synonyms, type specimens, type localities, and what is known about life histories, distributions, phenologies, and habitats of the species are given. Representative specimens are cited.