The monograph of famous theoretical physicists A.A. Varlamov and A.I. Larkin can serve as both an encyclopedia and a textbook on the theory of fluctuation phenomena in superconductors. Its first half is devoted to a detailed presentation of the phenomenological methods of Ginzburg-Landau theory and microscopic methods of quantum field theory in describing fluctuation. In the second half of the book, the authors present a broad picture of the manifestations of superconducting fluctuations in various observed quantities, their role in such relevant areas as high-temperature superconductivity, Josephson structures, superconducting nano-objects, granular superconductors, highly disordered systems. Reading most existing textbooks gives the impression that the BCS superconductivity theory is accurate. The proposed monograph dispels this misconception by clearly pointing to the limits of applicability of mean-field theory and the existence of a vast range of phenomena beyond it.