It's our great pleasure to welcome you to the 2018 ACM International Conference on Intelligent User Interfaces (IUI 2018), held in Tokyo from 7-11 of March. This is the twenty-third IUI conference, continuing its tradition of being the main international forum for reporting outstanding research at the intersection of Human Computer Interaction (HCI) and Artificial Intelligence (AI). The work that appears at IUI bridges these two fields and delves also into related fields, such as psychology, cognitive science, computer graphics, the arts, and others. Members of the IUI community are interested in improving the symbiosis between humans and computers, and in making systems adapt to humans rather than the other way around. The program of IUI 2018 reflects the growth of the Intelligent User Interfaces research community. The calls for contributions attracted 297 full and short paper submissions from all over the world (a record number for the IUI conference series), 127 submissions of posters and demos, and 22 submissions to the student consortium. The conference committee accepted 68 papers (43 long papers and 25 short papers), covering a diverse range of topics, as reflected in the conference session titles. The conference program also includes 35 posters, 30 demos, and 11 student consortium papers. Building on the tradition of collaboration of IUI with ACM TiiS journal, 4 papers that were published by the journal in 2017 will be presented at the conference and selected papers presented at the conference will be invited to submit extended versions to the journal. In addition, IUI 2018 will feature 7 workshops on topics related to Intelligent User Interfaces. One of the main features of the conference are the 3 keynote talks. James A. Landay from Stanford University will open the conference with a keynote talk entitled From On Body to Out of Body User Experience. Following this, Masataka Goto from the National Institute of Advanced Industrial Science and Technology (AIST) will present his talk Intelligent Music Interfaces. Finally, Jennifer Golbeck from the University of Maryland will present her talk Surveillance or Support: When Personalization Turns Creepy. IUI 2018 will also feature the second edition of the lasting Impact Award, celebrating an impactful paper presented at one of the past editions of IUI. A novel aspect of IUI 2018 will be its co-location with IPSJ Interaction 2018, the leading domestic HCI conference in Japan. The two conferences will be held in the Hitotsubashi Hall and will be scheduled back-to-back, allowing the participants of one conference to also take part in the other. The two conferences will have a shared day that will feature the keynote talk of James A. Landay and a shared interactive poster/demo session. This co-location of the conferences will expose IUI to the local research community and hopefully attract new participants. We thank the IPSJ (Information Processing Society in Japan), and especially the five special-interest groups that organize IPSJ Interaction: IPSJ SIG-HCI, SIG-GN, SIG-UBI, SIG-EC and SIG-DCC. Without their immense help, this co-location would not have been possible. We also thank SIGCHI for their funding for Internationalisation, Diversity and Inclusion events at SIGCHI Sponsored Conferences to support this co-location.