An intensive survey of bees (Hymenoptera: Apoidea: Anthophila) on Martha's Vineyard, the largest offshore island in Massachusetts, USA, was conducted mostly from 2010–2011 at over 60 sites across the island's six towns. From over 14,500 specimens collected, processed and databased, we document 182 bee species in 31 genera. Historical records of an additional four species were identified from museum collections. Most bee specimens were collected from trap lines of bee bowls deployed to maximize coverage of habitats, and many others by direct collection targeting known host plants of pollen specialists (oligoleges) and their cleptoparasites. The island's fauna is more species-rich and includes a diverse assemblage of sand-nesting specialists (psammophiles) and pollen specialists with broader botanical associations than the recorded faunas of other regional islands. Notable finds include the first records of Anthophora walshii Cresson from the northeastern USA since the 1970s; two oligoleges of Maleberry Lyonia ligustrina (L.), Colletes productus Robertson and Melitta melittoides (Viereck); the parasitic Nomada rodecki Mitchell, newly associated with M. melittoides and newly placed within the Nomada basalis species group (previously associated with Melitta in Europe); and two species (in addition to N. rodecki) newly recorded from Massachusetts: Andrena neonana Viereck and Nomada xanthura Cockerell. We note 23 species not recorded from other Massachusetts offshore islands, of which 19 were unrecorded from southeastern Massachusetts. Two bumble bee species in the nominate subgenus Bombus, B. affinis Cresson and B. terricola Kirby, that have undergone regional declines were recorded historically from Martha's Vineyard and nearby islands but not found in this survey. Tables and figures are provided to summarize the phenology, taxonomic and behavioral composition of the island's bee fauna, which are discussed with reference to the faunas of Massachusetts, New York, and comparable mainland and island sites. As with other studies employing extensive bee bowl-trapping we found the most numerous species caught to be eusocial halictines. Our results underscore the role of maritime habitats underlain by sandy soils in sustaining regional diversity of bees in addition to Lepidoptera and other well-documented insect groups. Collection of a large proportion of pollen specialists and cleptoparasitic species from one but not both sampling years reinforces the need for multi-year studies of bee faunas.