The two-volume set LNCS 13950 and 13951 constitutes revised selected papers from the 27th International Conference on Financial Cryptography and Data Security, FC 2023, which was held from May 1-5, 2023, in Bol, Croatia.  The 39 full and 2 short papers presented in these proceedings were carefully reviewed and selected from 182 submissions. They were organized in topical sections as follows: Part I: Consensus; cryptographic protocols; decentralized finance;  Part II: Proof of X; Layer 2; attack techniques, defenses, and attack case studies; empirical studies and more decentralized finance; game theory and protocols.