This book constitutes the refereed proceedings of the 18th International Conference on Practice and Theory in Public-Key Cryptography PKC 2015 held in Gaithersburg MD USA in March/April 2015. The 36 papers presented in this volume were carefully reviewed and selected from 118 submissions. They are organized in topical sections named: public-key encryption; e-cash; cryptanalysis; digital signatures; password-based authentication; pairint-based cryptography; efficient constructions; cryptography with imperfect keys; interactive proofs; lattice-based cryptography; and identity-based predicate and functional encryption.