The 12th IFAC - IEEE International Workshop on Discrete Event Systems will be held on the campus of the école Normale Supérieure de Cachan, France, May 14-16, 2014. It will provide researchers from different fields (control theoreticians and control engineers, software engineers and computer scientists, operations research specialists) with an opportunity to exchange information and new ideas, and to discuss new developments in the field of DES theory and application.