This two-volume set (LNCS 16710-16711) constitutes the refereed proceedings of the 20th International Conference on Universal Access in Human-Computer Interaction, UAHCI 2026, held as part of the 28th International Conference, HCI International 2026, in Montreal, QC, Canada during July 26th to 31st, 2026. 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 proceedings published just before the start of the conference. The UAHCI 2026 proceedings were organized in topical sections as follows: Universal Access in Human-Computer Interaction (Part I): Design and Evaluation Methods and Tools for Universal Access; AI in Universal Access; Universal Access to Virtual and Augmented Reality; Universal Access to LearningUniversal Access in Human-Computer Interaction (Part II): Neurodiversity and Interaction; Sign Languages, Captions and Non-hearing Communication; Non-Visual Interaction; Universal Access to Health and Rehabilitation