In polar ecosystems, liquid water is one of the most limiting factors for life, thus organisms are mainly distributed in the places and times in which liquid water is present. Freshwater ecosystems are typically considered as oases for life in the polar desert and tundra biomes. The benthic component of these lakes, ponds, rivers, and streams is often rich in biodiversity as well as biomass. The main communities in the benthic habitat are microbial mats, aquatic mosses, and green algal felts that inhabit both running and lentic waters. The substantial primary production in these benthic autotrophic communities, together with their reduced losses of assimilated carbon because of the low temperatures, low degradation rates, and minimal grazing pressure, can result in luxuriant growth and accumulation of these photosynthetic elements. In this chapter, we first describe the types of communities typically found in non-marine benthic habitats. We then review the primary production rates that have been measured under different circumstances, drawing on information from the literature as well as unpublished results. We conclude the chapter by exploring why the benthic component (phytobenthos) often dominates over planktonic communities (phytoplankton) in polar aquatic ecosystems.