Permanent lava lakes are a quite unusual eruptive feature. Only half a dozen have so far been discovered and more or less closely studied. Only two presently exist. Lava lakes (that differ basically from temporary lava ponds or lava pools) are of great significance because they allow close observations of important phenomena accompanying volcanic eruptions that cannot be studied on 'normal' volcanoes: dormant ones simply do not manifest these phenomena and erupting ones usually do not allow close enough observations. According to the data collected by the present author over 45 years of investigations, lava lakes are thought to represent the uppermost level of convection currents that stir molten, gas-rich, magmas. Degassing appears either as powerful jets of high-pressure, high-speed exsolved volatiles escaping through wide-open vents or as either quiet exhalation through microscopic pores in the plastic, half molten silicate membrane that covers the surface of the lake when it is calm, or as more or less impressive 'lava fountains'.