The book provides an overview of the author's work devoted to experimental study of hopping conductivity, which includes substantial contributions, such as solving the problem of critical indices of the metal-insulator transition in doped semiconductors, investigation of transitions from different kinds of hopping conductivity, development of the "hopping spectroscopy" method that allows to reveal the details of the density-of-states near the Fermi level - appearance of a hard "magnetic gap", temperature induced smearing of the soft Coulomb gap, the "phononless" hopping and so on. A separate...