The two-volume set LNCS 16491 + 16492 constitutes the proceedings of the 17th International Workshop on Post-Quantum Cryptography, PQCrypto 2026, held in Saint Malo, France, during April 2026.The 27 full papers presented in the proceedings were carefully selected and reviewed from 66 submissions. These papers have been organized in the following topical sections:Part I: Quantum Algorithms and Quantum Security; Code-Based Cryptography; Lattice-Based Cryptography; and PQC Signatures and Implementation Techniques.Part II: Isogeny- and Group-Action-Based Cryptography; Cryptographic Protocols and PQC Transition; Code-Based Attacks; and Cryptanalysis and Fault Attacks.