This book constitutes the refereed proceedings of the 15th International Conference on Augmented Cognition, AC 2021, held as part of the 23rd International Conference, HCI International 2021, held as a virtual event, in July 2021.The total of 1276 papers and 241 posters included in the 39 HCII 2021 proceedings volumes was carefully reviewed and selected from 5222 submissions.AC 2021 includes a total of 32 papers; they were organized in topical sections named: BCI and brain activity measurement physiological measuring and human performance; modelling human cognition; and augmented cognition in complex environments.
