This book constitutes the proceedings of the Third International Joint Conference on Quantitative Evaluation of Systems and Formal Modeling and Analysis of Timed Systems, QEST+Formats 2026, which took place in Liverpool, UK, during September 2-4, 2026.

The 24 full papers included in this book were carefully reviewed and selected from 54 submissions.

They deal with up to date research in the quantitative evaluation and verification of systems, including fundamental and practical aspects of systems with quantitative nature (such as probability, timing, or cost) and particular focus on machine-learning and quantum systems, case studies, and tool papers.