The International Conference "Computer Algebra" was held online via Zoom on June 28-29, 2021 and the conference web-site is http://www.ccas.ru/ca/conference. Co-organized by the Dorodnicyn Computing Center of Federal Research Center "Computer Science and Control" of Russian Academy of Science and the Peoples' Friendship University of Russia, the conference was devoted to inspiring discussions on computer algebra and related topics. Researchers from different countries presented talks on their latest research work. This is the fourth edition of the conference, and the previous three were in 2016, 2017 and 2019, respectively.