This book constitutes the refereed proceedings of the 19th International Symposium on Theoretical Aspects of Software Engineering, TASE 2025, held in Limassol, Cyprus, during July 14–16, 2025.The 20 full papers, 1 short paper, 2 invited papers were carefully selected from 66 submissions.The papers present the latest developments in formal and theoretical software engineering methods and techniques.They are grouped in topical sections on program verification; verification and concurrency; SAT and SMT solving; trustworthy AI and system software; program analysis using machine learning; security; and dynamic analysis.