This book constitutes revised selected papers from the 12th International Conference on Critical Information Infrastructures Security, CRITIS 201, held in Lucca, Italy, in October 2017. The 21 full papers and 4 short papers presented were carefully reviewed and selected from 63 submissions. They present innovative research and explore new challenges in the field of critical information infrastructures protection (C(I)IP) and deal with multi-disciplinary approaches to relevant C(I)IP problems.