The eight-volume set, CCIS 2522-2529, constitutes the extended abstracts of the posters presented during the 27th International Conference on Human-Computer Interaction, HCII 2025, held in Gothenburg, Sweden, during June 22–27, 2025. The total of 1430 papers and 355 posters included in the HCII 2025 proceedings were carefully reviewed and selected from 7972 submissions. The papers presented in these eight volumes are organized in the following topical sections: Part I: Virtual, Tangible and Intangible Interaction; HCI for Health. Part II: Perception, Cognition and Interaction; Communication, Information, Misinformation and Online Behavior; Designing and Understanding Learning and Teaching experiences. Part III: Design for All and Universal Access; Data, Knowledge, Collaboration, Research and Technological Innovation. Part IV: Human-Centered Security and Privacy; Older Adults and Technology; Interacting and driving. Part V: Interactive Technologies for wellbeing; Game Design; Child-Computer Interaction. Part VI: Designing and Understanding XR Cultural Experiences; Designing Sustainable (Smart) Human Environments. Part VII: Design, Creativity and AI; eCommerce, Fintech and Customer Behavior. Part VIII: Interacting with Digital Culture; Interacting with GenAI and LLMs.