Twenty-four species of Orbiniidae, 12 new to science, are reported from continental shelf and slope (deep-sea) habitats of the western North Atlantic. The majority of new material was collected during reconnaissance and monitoring surveys along the entire U.S. Atlantic coast from New England to the Carolinas that were intended to understand the potential impacts of oil and gas exploration in poorly known offshore environments. Additional materials from shallow water and shelf habitats off New England and New York as part of other projects are also included. New collections of Califia schmitti (Pettibone, 1957), Leitoscoloplos acutus (Verrill, 1873), L. fragilis (Verrill, 1873), L. obovatus Mackie, 1987, L. robustus (Verrill, 1873), Scoloplos intermedius (Hartman, 1965), Orbinia swani (Pettibone, 1957), Phylo felix (Kinberg, 1866), P. norvegicus (Sars, 1872), P. ornatus (Verrill, 1873), and Questa trifurcata (Hobson, 1970) provide additional morphological details, variability, and extended geographic and bathymetric distributions of previously known species. New species include Leitoscoloplos pustulus n. sp., Scoloplos papillatus n. sp., S. pettiboneae n. sp., S. pseudoarmiger n. sp., S. verrilli n. sp., Leodamas cuneatus n. sp., L. mucronatus n. sp., L. notoaciculatus n. sp., Phylo paraornatus n. sp., Orbiniella acsara n. sp., O. armata n. sp., and O. mimica n. sp. Juveniles of some species of Leitoscoloplos and Scoloplos were found to resemble known species of the meiofaunal orbiniid genus Schroederella Laubier, 1962. As such, S. berkeleyi Laubier, 1971 is referred to synonymy with Leitoscoloplos acutus. More importantly, the genus Schroederella was found to be pre-occupied by Schroederella Enderlein, 1921 in the Insecta, Diptera, family Helomyzidae. Gesaschroederella nomen nov. is therefore proposed as a replacement name for the polychaete homonym.