This book constitutes the refereed proceedings of the 18th International Symposium on Formal Methods, FM 2012, held in Paris, France, in August 2012. The 28 revised full papers presented together with 7 tool papers and 3 invited talks were carefully reviewed and selected from numerous submissions. The papers cover several aspects of formal methods, including verification, synthesis, runtime monitoring, testing and controller synthesis, as well as novel applications of formal methods in interesting domains such as satellites, autonomous vehicles and disease dynamics.