This volume constitutes the proceedings of the 11th International Conference on post-quantum cryptography, PQCrypto 2020, held in Paris, France in April 2020. The 29 full papers presented in this volume were carefully reviewed and selected from 86 submissions. They cover a broad spectrum of research within the conference's scope, including code-, hash-, isogeny-, and lattice-based cryptography, multivariate cryptography, and quantum cryptanalysis.