[en] The proceedings of the seminar contain 19 contributions dealing with various problems of plasma diagnostics in tokamaks and thermonuclear reactors. The diagnostics and data acquisition systems being developed for direct use in the T-15 tokamak are discussed in 15 papers. Particularly, the submillimeter interferometer, X-ray, VUV and neutron spectrometers and the time-of-flight analyzer of neutrals are described in detail. Special attention is paid to nuclear diagnostic methods of fusion products, especially alpha particles. The other papers deal with Langmuir probe measurements in edge plasmas, with the influence of radiation on diagnostic systems and their components and with the general theoretical results on the lower hybrid current drive relevant to hot plasma diagnostics. (J.U.)