The book contains abstracts of oral and poster reports presented at the 15 International Conference "Gas Discharge Plasmas and Their Applications" (GDP 2021). This event is a continuation of conferences on gas discharge physics held in Russia since 1984, as well as seminars and conferences on the technological application of low-temperature plasma. The conference is held every 2 years in different cities of the Russian Federation. This year, the wonderful city of Ekaterinburg, located in the heart of the Urals on the border of Europe and Asia, was chosen as the venue. The program of the Conference covers a wide range of technical areas and modern aspects of the physical processes occurring in generators of low temperature plasma, low and high-pressure discharges, pulsed plasma sources, surface modification, and other gas-discharge technologies.