Polynyas are areas of open water that occur at specific, recurrent locations in the polar regions and that are surrounded by ice-covered waters. They have been of interest historically because they are centers of upper trophic level biological activity and were consequently foci of both commercial whaling activities and of native subsistence hunting. They have more recently become of interest from a basic research viewpoint because they are typified by intensive biological activity and energetic physical processes. They are similar, in many respects, to the marginal ice zones, which are an ongoing focus of considerable oceanographic research. Polynyas can be conceptually envisaged as polar oceanic “oases” in which biological activities are focused locally while they are surrounded by relatively unproductive waters. Polynyas serve as outposts of enhanced production within the pack ice remote from the biologically rich marginal ice zones.