This book constitutes the refereed proceedings of the 12th International Conference on Formal Modeling and Analysis of Timed Systems, FORMATS 2014, held in Florence, Italy, in September 2014. The 17 revised full papers presented were carefully reviewed and selected from 36 submissions. The papers cover topics of foundations and semantics; comparison between different models, such as timed automata, timed Petri nets, hybrid automata, timed process algebra, max-plus algebra, probabilistic models; methods and tools for analyzing timed systems and resolving temporal constraints; applications in real-time software, hardware circuits, and problems of scheduling in manufacturing and telecommunication.