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Jenő Sólyom, physicist and member of HAS, delves into the world of extremely low temperatures. As temperature is lowered, quantum effects become increasingly important. Close to absolute zero, condensed matter may give rise to unexpected properties, like superfluidity or superconductivity. If a system is composed of bosons, Bose-Einstein condensation may take place. In a free gas made up of alkali atoms held in a trap, Bose-Einstein condensation happens at extremely low temperatures. The superfluidity of 4He can be easily demonstrated in a laboratory. More important is the superconductivity in fermionic systems, since they allow for many industrial and medical applications. The recent discovery of high transition temperature superconductors will probably make all applications more widespread. This challenges physicists to better understand the mechanism that leads to superconductivity in these materials.