The phenomenon of superconductivity, discovered over 50 years and explained about 10 years ago, is becoming increasingly widespread. Experimental and theoretical studies of superconducting materials are also expanding. The book offered to readers by the French physicist De Zhen in a lively and physically clear form illuminates the most important properties of superconductors and modern theoretical ideas that underlie the interpretation of the observed effects and calculations of devices for practical applications. The book is aimed at physicists and engineers involved in experimental research on superconductors and students embarking on the study of superconductivity.