This book constitutes the proceedings of the 15th International Conference on Foundations of Software Science and Computational Structures, FOSSACS 2012, held as part of the joint European Conference on Theory and Practice of Software, ETAPS 2012, which took place in Tallinn, Estonia, in March/April 2012. The 29 papers presented in this book together with two invited talks in full paper length were carefully reviewed and selected from 100 full paper submissions. The papers deal with theories and methods to support analysis, synthesis, transformation and verification of programs and software systems.