The two-volume set LNCS 10677 and LNCS 10678 constitutes the refereed proceedings of the 15th International Conference on Theory of Cryptography, TCC 2017, held in Baltimore, MD, USA, in November 2017. The total of 51 revised full papers presented in the proceedings were carefully reviewed and selected from 150 submissions. The Theory of Cryptography Conference deals with the paradigms, approaches, and techniques used to conceptualize natural cryptographic problems and provide algorithmic solutions to them and much more.