This book constitutes the proceedings of the 20th International Conference on Foundations of Computer Science, FCS 2024, and the 20th International Conference on Frontiers in Education, FECS 2024, held as part of the 2024 World Congress in Computer Science, Computer Engineering and Applied Computing, in Las Vegas, USA, during July 22 to July 25, 2024. The 10 FECS 2024 papers included were carefully reviewed and selected from 43 submissions. FCS 2024 received 172 submissions and accepted 31 papers for inclusion in the proceedings. The papers have been organized in topical sections as follows: Foundations of computer science; frontiers in education - novel studies and assessment results; frontiers in educations - tools; frontiers in education - student retention, teaching and learning methods, curriculum design and related issues; and poster/position papers. .