This two-volume set LNCS 10907 and 10908 constitutes the refereed proceedings of the 12th International Conference on Universal Access in Human-Computer Interaction, UAHCI 2018, held as part of HCI International 2018 in Las Vegas, NV, USA, in July 2018. The total of 1170 papers and 195 posters included in the 30 HCII 2018 proceedings volumes was carefully reviewed and selected from 4373 submissions. The 49 papers presented in this volume were organized in topical sections named: design for all, accessibility and usability; alternative I/O techniques, multimodality and adaptation; non-visual interaction; and designing for cognitive disabilities.