The two-volume proceedings set LNCS 12710 and 12711 constitutes the proceedings of the 24th IACR International Conference on Practice and Theory of Public Key Cryptography, PKC 2021, which was held online during May 10-13, 2021. The conference was originally planned to take place in Edinburgh, UK, but had to change to an online format due to the COVID-19 pandemic.The 52 papers included in these proceedings were carefully reviewed and selected from 156 submissions. They focus on all aspects of public-key cryptography, covering theory, implementations and applications. This year, post-quantum cryptography, PQC constructions and cryptanalysis received special attention.