This book constitutes the refereed proceedings of the 12th International Conference on Code-Based Cryptography, CBCrypto 2024, held in Zurich, Switzerland, during May 25-26, 2024. The 5 full papers presented in this book were carefully reviewed and selected from 41 submissions. The conference offers a wide range of many important aspects of code-based cryptography such as cryptanalysis of existing schemes, the proposal of new cryptographic systems and protocols as well as improved decoding algorithms.