This book constitutes the refereed proceedings of the 20th International Symposium on Theoretical Aspects of Software Engineering, TASE 2026, held in Shanghai, China, during July 4–6, 2026.The 23 full papers and 5 short papers were carefully selected from 64 submissions. The proceedings aim to bring together researchers and developers from academia and industry with interest in the theoretical aspects of software engineering.

This book constitutes the refereed proceedings of the 20th International Symposium on Theoretical Aspects of Software Engineering, TASE 2026, held in Shanghai, China, during July 4–6, 2026.The 23 full papers and 5 short papers were carefully selected from 64 submissions. The proceedings aim to bring together researchers and developers from academia and industry with interest in the theoretical aspects of software engineering.