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 chapter is devoted to the hopping photoconductivity and inter-impurity radiative recombination of non-equilibrium carriers. This book is suitable for undergraduate and graduate students in physics, researchers in semiconductor electronics and even for the non-experts who wish to have a notion about hopping mechanism of transport. The explanations in the book are simple and detailed enough to capture the interest of the curious reader.