This book constitutes the refereed post-conference proceedings of the 20th International Conference on Computer Science and Education in Computer Science, CSECS 2024, held in Sofia, Bulgaria, during June 28-30, 2024. The 19 full papers and 4 short papers were carefully reviewed and selected from 49 submissions.The papers cover the following topics: Computer Science Implementations; Computational Math; Computing Technologies; Implementations in Medicine; Engineering Implementations; Education in Computer Science.