The book collects and systematizes the results of observations of the activity of the most common variable stars of the Galaxy - flashing stars of the UV Keith type: the results of photometric and spectral observations of optical flares, characteristics of the radio and X-ray bursts accompanying them, data on the slowly changing emission spectrum associated with stellar chromospheres, and on small fluctuations in brightness "arising from the uneven surface brightness of these stars. The results of the theoretical analysis of the observed phenomena are presented, with particular attention paid to the proof of the thesis on the identity of the physical nature of solar activity and the activity of stars of the UV Keith type and the justification of the concept of flashing stars as magnetic stars of small masses. Stellar and astronomical characteristics of flashing stars and problems of evolution of these objects are considered. Given a catalog of UV Keith stars in the vicinity of the Sun.