TCC 2008, the 5th Theory of Cryptography Conference, was held in New York, New York, March 19-21, 2008, at New York University. TCC 2008 was sp- soredbytheInternationalAssociationforCryptologicResearch(IACR)andwas organizedincooperationwiththeDepartmentofComputerScienceatNewYork University and the Courant Institute for Mathematical Sciences. The General Chairs of the conference were Yevgeniy Dodis and Victor Shoup. The conference received 81 submissions, of which the Program Committee selected34forpresentationattheconference.Theauthorsoftwopapersthen- cidedto mergetheir papers,resulting in a totalof33 presentedpapers.The Best Student Paper Award was given to Paul Valiant for his paper "Incrementally Veri?able Computation or Knowledge Implies Time/Space E?ciency." These proceedings consist of revised versions of the presented papers. The revisions were not reviewed. The authors bear full responsibility for the contents of their papers. The conference programalso included four special events: an invited talk - titled "Randomness Extractors and Their Cryptographic Applications" by Salil Vadhan; a tutorial entitled "Bridging Cryptography and Game Theory: Recent Results and Future Directions," given by Jonathan Katz (with an accom- nying tutorial in the proceedings); a panel discussion on "Game Theory and Cryptography: Towards a Joint Point of View?" with Tal Rabin as moderator and Jonathan Katz, Silvio Micali, and Moni Naor as panelists; and a Rump Session chaired by Anna Lysyanskaya.