This book constitutes the refereed proceedings of the 13th International Conference on Provable Security, ProvSec 2019, held in Cairns, QLD, Australia, in October 2019.  The 18 full and 6 short papers presented were carefully reviewed and selected from 51 submissions. The papers focus on provable security as an essential tool for analyzing security of modern cryptographic primitives, including a special theme on “Practical Security.”