In August 2007, a whalebone mask was excavated from a 3,000-year-old settlement site in the eastern Aleutian Islands, Alaska. Although wooden masks are ethnographically common and well-documented from most other regions of coastal Alaska, examples made from bone or other materials are quite rare. The uses and significance of prehistoric masks are difficult to ascertain. Russians, the first Europeans to visit the Aleutian Islands, recorded ritual and ceremonial use of masks by indigenous inhabitants during the latter half of the eighteenth century. Ceremonial mask use is also known from related cultures, especially Yup'ik and Inupiat Eskimos as well as Sugpiaq peoples (Kodiak Islanders). This investigation describes the Amaknak mask and the circumstances of its discovery, and draws on comparative material from local and neighboring regions for analysis and interpretation of the mask. Although conclusions remain speculative, the Amaknak mask likely offers a glimpse at prehistoric Aleutian ritual and spiritual life.