This book constitutes the refereed proceedings of the 12th International Conference on Rigorous State-Based Methods, ABZ 2026, held in Tokyo, Japan, during May 2026.The 15 full papers, 3 short papers and 2 ABZ 2026 case study papers presented in this book were carefully reviewed and selected from 25 submissions.The ABZ conference series is dedicated to the cross-fertilization of state-based and machine-based formal methods. Abstract State Machines (ASM), Alloy, B, TLA, VDM, and Z are examples of these methods. They share a common conceptual foundation and are widely used in both academia and industry for the rigorous design and analysis of hardware and software systems. The ABZ conferences aim to be a forum for the vital exchange of knowledge and experience among the research communities around different formal methods.

This book constitutes the refereed proceedings of the 12th International Conference on Rigorous State-Based Methods, ABZ 2026, held in Tokyo, Japan, during May 2026.The 15 full papers, 3 short papers and 2 ABZ 2026 case study papers presented in this book were carefully reviewed and selected from 25 submissions.The ABZ conference series is dedicated to the cross-fertilization of state-based and machine-based formal methods. Abstract State Machines (ASM), Alloy, B, TLA, VDM, and Z are examples of these methods. They share a common conceptual foundation and are widely used in both academia and industry for the rigorous design and analysis of hardware and software systems. The ABZ conferences aim to be a forum for the vital exchange of knowledge and experience among the research communities around different formal methods.