This book constitutes the refereed proceedings of the 21st EAI International Conference on Computer Science and Education in Computer Science, CSECS 2025, held in Bratislava, Slovak Republic, during July 1–3, 2025.

The 18 full papers and 7 short papers included in this book were carefully reviewed and selected from 104 submissions. They are organized into the following topcial sections: Education in Computer Science; Computer Science Technologies; Computer Science Implementation in Medicine and Computer Science Implementation in Industry.