The Russian open scientific conference “Modern problems of remote sensing, radar, wave propagation and diffraction” (MPRSRWPD) 2021 took place in the Russian Federation in the city of Murom on May 25-27, 2021.The conference has been held at the Murom Institute of Vladimir State University since 1991. The organizers of the Conference MPRSRWPD 2021 are the Russian Academy of Sciences, diverse scientific organizations and a number of leading universities of Russia.Unfortunately, the COVID pandemic limited the travel of scientists and personal participation in the conference. Under these conditions, the Organizing Committee decided to hold MPRSRWPD 2021 completely online with remote meeting control from the Murom Institute.Such a decision required a different organization of the conference itself, the need for more precise compliance with the schedule for presentations, taking into account the differences between the time zones in which the speakers were located. Thanks to the efficient work of the Organizing Committee, these difficulties were successfully overcome.Of course, this format of the conference significantly narrowed the opportunities for personal communication of participants, practically eliminating discussions during breaks and after the end of meetings, which has always been an indispensable attribute of this conference. Nevertheless, the discussion of the reports took place, and at the end of the meetings, a general discussion took place in the format of a “round table”.Sixty two reports on the issues of wave propagation and diffraction, remote sensing, methodological and instrumental issues of sounding, and measurement accuracy were presented at the conference. Thirty four papers of them were recommended by the Program and Organizing Committees for publication in the JPCS collection. Twenty eight articles based on the results of peer review met the standards of IOP Publishing.The Organizing Committee expresses its gratitude to everyone who, at this difficult time, managed to find opportunities to participate in the conference, to everyone the organization of the work of the meetings depended on, and especially to our esteemed experts-I. Nasyrov, PhD, Associate Professor, A. Padokhin, PhD, Associate Professor, V. Pozhidaev, Doctor of Physics and Mathematics, Chief Researcher, B. Sedunov, PhD, Associate Professor, and I. Yusupov, PhD, Associate Professor, whose high qualifications ensured the compliance of the scientific level of the submitted articles with the requirements of IOP Publishing.We express our sincere regret that Yuri Ya. Ruzhin, Doctor of Physics and Mathematics, Professor, Chief Researcher, recipient of the State Prize of the Russian Federation, Member of the National Geophysical Committee, one of the active organizers of our conferences for many years, passed away during the preparation of the Conference. We would like to extend our heartfelt condolences to his family and colleagues.On behalf of the Organizing Committee, Committees, Organizing Committee, Executive editor, are available in the pdf