The book is devoted to one of the many areas of gas discharge physics - breakdown at atmospheric pressures. It contains brief theoretical and experimental data on various elementary processes occurring in a gas-discharge plasma. Information on the development of the discharge is successively presented, starting from the appearance of the primary electron and until the discharge gap is closed by the ionized channel. The book is aimed at senior students and graduate students specializing in the fields of physics related to gas discharge, as well as experimenters working with streamer chambers and other gas discharge devices.