The phenomenon of superconductivity, fist discovered by Kamerlingh Onnes in 1911, offers considerable fundamental interest as an unusual example of quantum effects on a macroscopic scale and of interest also in respect of its possible technological applications. Although Dr Shoenberg's classic monograph was written in 1938, before the great burst of activity which followed the development of a fundamental theory of superconductivity, its phenomenological description of the magnetic and thermodynamic properties and of size effects in superconductors, which are taken for granted in most accounts, are essential parts of the subject which must be properly understood before the newer ideas can really be appreciated. Reissued in 1952 and again in 2010, the book will continue to serve therefore as an intriguing study in this field and for those interested in superconductivity.