The book comprises high-quality refereed research papers presented at the Third International Symposium on Computer Science, Digital Economy, and Intelligent Systems (CSDEIS2021), held in Moscow, Russia, on December 25-26, 2021, organized jointly by the Mechanical Engineering Research Institute of the Russian Academy of Sciences，Moscow State Technical University, and the International Research Association of Modern Education and Computer Science. The topics discussed in the book includes state-of-the-art papers in computer science and their technological applications; intelligent systems and intellectual approaches; digital economics and methodological approaches. It is an excellent source of references for researchers, graduate students, engineers, management practitioners, and undergraduate students interested in computer science and its applications in engineering and management.