The 18th InternationalConference on User Modeling, Adaptation and Person- ization(UMAP 2010)took placeon BigIsland, HawaiiduringJune 20-24,2010. It was the second conference after UMAP 2009 in Trento, Italy, which merged the successful biannual User Modeling (UM) and Adaptive Hypermedia (AH) conference series. The ResearchPapertrackof the conferencewaschairedbyPaulDe Brafrom the Eindhoven University of Technology and Alfred Kobsa from the University ofCalifornia,Irvine. TheywereassistedbyaninternationalProgramCommittee of 80 leading ?gures in the AH and UM communities as well as highly promising youngerresearchers. Papersinthe ResearchPapertrackweregenerallyreviewed by three and sometimes even four reviewers, with one of them acting as a lead who initiates a discussion between reviewers and reconciles their opinions in a meta-review. The conferencesolicitedLong ResearchPapersof up to 12pagesin length, whichrepresentoriginalreports of substantivenew research. In addition, theconferenceacceptedShortResearchPapersofuptosixpagesinlength,whose merit was assessed more in terms of originality and importance than maturity and technical validation. The Research Paper track received 161 submission, with 112 in the long and 49 in the short paper category. Of these, 26 long and 6 short papers were accepted, resulting in an acceptance rate of 23. 2% for long papers and 19. 9% overall. Many authors of rejected papers were encouraged to resubmit to the Poster and Demo track of the conference. Following the example of UMAP 2009, the conference also had an Ind- try Paper track chaired by Bhaskar Mehta from Google, Zur ¨ ich, Switzerland and Kurt Partridge from PARC, Palo Alto, USA.