The contains the results of investigations and diagnostics of electrophysical, gas-dynamic, chemical and other processes in low-temperature plasma. Both conventional spectral and optical methods of diagnostics and new laser methods are examined, together with electrostatic probes for investigating rarefied and dense plasma, especially in the presence of chemical reactions. Problems of the probe calorimetry of plasma flows are investigated and approaches to measuring the spatial and time characteristics of plasma are outlined. Procedural problems of processing experimental data and automatic diagnostic experiments are also discussed.