[en] Since its discovery in 1911, superconductivity has been one of the most actively studied fields in condensed matter physics and has attracted immense experimental and theoretical effort. At this point in time, with more and more superconductors discovered in elements, alloys, intermetallic compounds and oxides, it is becoming clear that superconductivity is actually not so rare in nature. Almost half of the elements in the periodic table and hundreds of compounds have been found to be superconducting. Fig. 1.1 shows the milestones in discovering higher T_c superconductors. Among the elemental superconductors, Niobium has the highest superconducting transition temperature, T_c, of 9.5 K. This record held for more than ten years, until the discovery of niobium nitride which superconducts below 16 K. It took another thirty years for T_c to increase from 16 K in niobium nitride to 23 K in niobium germanium.