At the floor of the Antarctic ice sheet, 4 km below the Russian research base Vostok Station, lies a 2,000 km3 body of water, comparable in size to Lake Ontario. This remote water mass, named Lake Vostok, is the world's largest subglacial lake by an order of magnitude (Figure 1). Despite ice-surface temperatures regularly around -60 degrees C, the ice-sheet base is kept at the melting temperature by geothermal heating from the Earth's interior. The ice sheet above the lake has been in existence for at least several million years and possibly as long as 20 million years. The origins of Lake Vostok may therefore data back across geological time to the Miocene (7-26 Ma). The hydrology of Lake Vostok can be characterised by subglacial melting across its northern side, and refreezing over the southern section. A deep ice core, located over the southern end of the lake has sampled the refrozen ice. Geochemical analysis of this ice has found that it comprises virtually pure water. However, normal glacier ice contains impurities such as debris and gas hydrates. Subglacial melting and freezing over Lake Vostok may, therefore, leave the lake enriched in potential nutrients issued from the melted glacier ice. Many scientists expect microbial life to exist within the lake, adapted to the extreme conditions of low nutrient and energy levels. Indeed microbes have been found in the basal refrozen layers of the ice sheet. If Lake Vostok has been isolated from the atmosphere for several million years by the ice sheet that lays above it, the microbes within the lake must also date back several million years and may have undergone evolution over this time, yielding life that may be unique to Lake Vostok. Plans are currently being arranged to explore Lake Vostok and other Antarctic subglacial lakes, and identify life in these extraordinary places. Before this happens, however, much more needs to be known about the ice-sheet above subglacial lakes, and the rocks and sediment below them.