The author of this unique volume, Lev P Gor'kov is internationally renowned for his seminal contribution in the fundamentals of the Theory of Superconductivity, Theory of Metals, the field of Quantum Statistical Physics, and more generally, Organic Metals and the like. Each reprints' group is preceded by the author's introductions and commentaries clarifying the formulation of a problem, summarizing the essence of the results and placing them in the context of recent developments. The author belongs to the last generation of scientists who were the direct disciples of the legendary Russian theorist Lev Landau. And Gor'kov's achievements reflect the unique style and the originality of this famous Scientific School. As with other Russian scientists of his generation, many of the pioneering papers by Lev Gor'kov have been published in the Russian journals that are hard-to-reach for modern readers, students and postdocs. Allowing readers a glimpse into the various ways that the field of condensed matter physics was evolving for more than half a century, the volume is a valuable source for historians of science.