This book set constitutes the refereed proceedings of the Human-Computer Interaction thematic area of the 28th International Conference on Human-Computer Interaction, HCII 2026, held in Montreal, Canada, during July 26-31, 2026.The HCI Thematic Area constitutes a forum for scientific research and addressing challenging and innovative topics in Human-Computer Interaction theory, methodology and practice, including, for example, novel theoretical approaches to interaction, novel user interface concepts and technologies, novel interaction devices, UI development methods, environments and tools, multimodal user interfaces, emotions in HCI, aesthetic issues, HCI and children, evaluation methods and tools, and many others. A total of 7435 individuals from academia, research institutes, industry, and government agencies from 94 countries submitted contributions to HCII 2026. Following peer review, 1463 papers and 360 posters (as short research papers) are included in the volumes of the HCII 2026 proceedings published just before the start of the conference.Four volumes (LNCS 16701 - 16704) of the HCII 2026 proceedings are dedicated to the HCI Thematic Area this year focusing on topics related to:HCI Methods, Theories, and Design Research; Psychology, Emotion, and Human Behavior; Ethics, Inclusivity, and Critical HCI;Interaction Design for Social, Companion, and Assistive Robots; Human-AI Interaction and Multi-Agent Systems; Immersive Interaction and Extended Reality Experiences;Interaction Design for Conversational Agents; Designing Interactive and AI-Driven Systems for Health and Well-Being; and Human-Centered Design for Learning and Creativity;Perception, Visualization, and Sensemaking in HCI; Advanced Interaction Techniques and Sensing Technologies; and Applied User-Centered Interaction Design and HCI Systems.
