I am indeed pleased to prepare this brief foreword for this book, written by several of my friends and colleagues in the Soviet Union. The book was first published in the Russian language in Moscow in 1975. The phenomenon of superconductivity was discovered in 1911 and promised to be important to the production of electromagnets since superconductors would not dissipate Joule heat. Unfortunate­ ly the first materials which were discovered to be superconducting reverted to the normal resistive state in magnetic fields of a few tesla. Thus the development that was hoped for by hundredths of a the early pioneers was destined to be delayed for over half a century. In 1961 the intermetallic compound NbaSn was found to be superconducting in a field of about 200 teslas. This breakthrough marked a turning point, and 50 years after the discovery of superconductivity an intensive period of technological development began. There are many applications of superconductivity that are now being pursued, but perhaps one of the most important is super­ conducting magnetic systems. There was a general feeling in the early 1960s that the intermetallic compounds and alloys that were found to retain superconductivity in the presence of high magnetic fields would make the commercialization of superconducting magnets a relatively simple matter. However, the next few years were ones of disillusionment; large magnets were found to be unstable, causing them to revert to the normal state at much lower magnetic fields than predicted.