This book constitutes the refereed proceedings of the 29th International Conference on Engineering of Complex Computer Systems, ICECCS 2025, which took place in Hangzhou, China, during July 2-4, 2025.

The 21 full papers, 3 short papers and 8 position papers included in this book were carefully reviewed and selected from 70 submissions. They were organized in topical sections as follows: Machine Learning for Complex Systems; Trustworthy Deep Learning; Edge Computing Systems; Large Language Models Empowered Software Engineering; Formal Methods; Program Analysis; Position Papers: Large Language Model Agents; Position Papers: Software Engineering for Large Language Models; and Position Papers: Large Language Models for Software Engineering. set programming; functional programming; languages, methods and tools; and declarative solutions.