The 3 volume-set LNCS 10901, 10902 + 10903 constitutes the refereed proceedings of the 20th International Conference on Human-Computer Interaction, HCI 2018, which took place in Las Vegas, Nevada, in July 2018. The total of 1171 papers and 160 posters included in the 30 HCII 2018 proceedings volumes was carefully reviewed and selected from 4346 submissions. HCI 2018 includes a total of 145 papers; they were organized in topical sections named: Part I: HCI theories, methods and tools; perception and psychological issues in HCI; emotion and attention recognition; security, privacy and ethics in HCI. Part II: HCI in medicine; HCI for health and wellbeing; HCI in cultural heritage; HCI in complex environments; mobile and wearable HCI. Part III: input techniques and devices; speech-based interfaces and chatbots; gesture, motion and eye-tracking based interaction; games and gamification.