This book constitutes the revised selected papers fromthe 12th International Conference on Formal Aspects of Component Software, FACS2015, held in Niterói, Brazil, in October 2015.The 15 full papers and 2 invited papers presented in thisvolume were carefully reviewed and selected from 33 submissions. They areorganized in topical sections, namely quality of service to withstand faults,component-based software development through research on mathematical modelsfor components, composition and adaptation; rigorous approaches toverification, deployment, testing, and certification.