ThisvolumecontainstheproceedingsofMPC2008, the9thInternationalConf- enceontheMathematicsofProgramConstruction.Thisseriesofconferencesaims to promote the development of mathematical principles and techniques that are demonstrably useful in the process of constructing computer programs, whether implemented in hardware or software. The focus is on techniques that combine precision with conciseness, enabling programs to be constructed by formal c- culation.Within this theme, the scopeofthe seriesisverydiverse, including p- grammingmethodology, programspeci?cationandtransformation, programming paradigms, programmingcalculi, andprogramminglanguagesemantics. The quality of the papers submitted to the conference was in general very high, and the number of submissions was comparable to that for the previous conference. Each paper was refereed by at least four, and often more, committee members. This volume contains 18 papers selected for presentation by the Program Committee from 41 submissions, 1 invited paper which was reviewed as well, and the abstracts for two invited talks. The conference took place in Marseille-Luminy, France. The previous eight conferences were held in 1989 in Twente, The Netherlands; in 1992 in Oxford, UK; in 1995 in Kloster Irsee, Germany; in 1998 in Marstrand near Got ] eborg, Sweden; in 2000 in Ponte de Lima, Portugal; in 2002 in Dagstuhl, Germany; in 2004, in Stirling, UK; and in 2006 in Kuressaare, Estonia. The proceedings of these conferences were published as LNCS 375, 669, 947, 1422, 1837, 2386, 3125 and 4014, respectively. We aregratefulto the members ofthe ProgramCommittee andtheir referees for their care and diligence in reviewing the submitted pa