The four-volume set LNCS 6946-6949 constitutes the refereed proceedings of the 13th IFIP TC13 International Conference on Human-Computer Interaction, INTERACT 2011, held in Lisbon, Portugal, in September 2011. The 47 papers included in the first volume are organized in topical sections on accessibility, affective HCI, computer-mediated communication, computer-supported cooperative work, evaluation, finding and retrieving, fun/aesthetic design, gestures, and HCI in the classroom.