In accordance with the task given to the Soviet Geodynamic Expedition and aimed at elucidation of the relationship of Iceland to the adjacent structures of the oceanic bottom, three forms of recent geothermal activity of Iceland have been studied: the background conductive heat flow, hydrothermal activity and volcanism. It has been established that the thermal conductivity of basalts in Iceland is, on an average, 3.62 · 10 −3 cal/cm.sec.°C. The geothermal field abounds in local anomalies caused by the circulation of hydrothermae. The background conductive heat flow decreases to 1.2–1.6 HFU in regions of old plateau-basalts in the northwest and east of Iceland and has a submeridional maximum (> 2.2 HFU) in the centre of the island. Deep temperatures are 300–700°C higher than in stable structures of the oceanic bottom. This may prove one of the factors responsible for lowering of the “mantle” velocities of P- waves observed beneath Iceland. In their gas composition, the thermal fluids are divided into nitrogenous, carbon-dioxide, nitrogen-carbon-dioxide and hydrogenous. The latter, being representative of the hydrothermal activity of Iceland, are the most powerful high-temperature hydrothermal systems associated with the Median zone. The distribution of geochemical types of fluids is subject to a well-pronounced zonation coinciding with the geostructural pattern of the island and zonation of the heat effect of hydrothermal discharge. The heat power of nitrogen-carbon-dioxide and hydrogenous thermae shows the participation of deep heatcarriers in their formation. The effect of hydrothermal activity in the Median zone varies within 1.5 and 5.0 HFU. The isotopic contents of He, Ar and S contained in thermal fluids confirms the presence of mantle emanations in them (the 3He/ 4He ratio reaches 3.3 · 10 −5, δ 40Ar = 12%, δ 34S ≈ 0%.) and testifies to difference of the Icelandic crust from the continental crust in composition. This conclusion is supported by low mineralization of thermal fluids characterized by the extremely minor role of chlorides. Individual volcanic centres are characterized by powers of the order of n · 10 8 cal/sec, the fluctuations in which coincide with changes of the character of the productivity. The total energetic effect of Quaternary volcanism in the Median zone is at the level of 3–5 HFU, with variations in place and time, however, of up to 8 HFU. Comparison of the data obtained with the observed and theoretical distribution of the heat outflow in the mid-oceanic ridges shows that the dynamics and scale of the convective heat-mass transfer in the axial zones of these structures are not estimated under submarine conditions and ignored by the models available.