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Biological soil crusts have been extensively studied in arid lands of temperate regions, particularly semi-arid steppes and warm deserts. Arctic soil crusts have received some attention, but they are far less studied than their temperate counterparts. While the tundra zone of Arctic regions has an abundant cover of lichens, mosses and low-growing vascular plants, the High Arctic semi-arid and arid deserts have a much reduced but still very significant cover of biological soil crust dominated by microalgae. This review discusses what is known about Arctic soil crusts with the intention of stimulating study of this sensitive ecosystem. Arctic soil crusts are considered to be one of the most extreme habitat types on earth. Low temperatures and lack of water associated with a wide spectrum of disturbances have a dramatic effect on chemical and physical soil ecological properties (salinity, pH, conductivity and gas content). Microalgae are the keystone microbial species in polar crusts, being significant primary producers, fixing atmospheric nitrogen and secreting polysaccharides that bind soil aggregates together, thereby reducing erosion and water runoff. The biological diversity of soil crust microalgae in the Arctic is high. Soil crusts of the Arctic semi-arid and arid deserts provide a special opportunity to study the environmental factors controlling the diversity, distribution and abundance of the microalgae in the absence of anthropogenic disturbance. However, anthropogenic disturbances and climate change are occurring in the Arctic, and even more transformations are expected in the near future. Therefore, the ecological study of Arctic ecosystems, including biological soil crusts, is a matter of urgency.