This book constitutes the proceedings of the 9th International Conference on the Foundations of Augmented Cognition, AC 2015, held as part of the 17th International Conference on Human-Computer Interaction, HCII 2015, which took place in Los Angeles, CA, USA, in August 2015. HCII 2015 received a total of 4843 submissions, of which 1462 papers and 246 posters were accepted for publication after a careful reviewing process. These papers address the latest research and development efforts and highlight the human aspects of design and use of computing systems. The papers thoroughly cover the entire field of Human-Computer Interaction, addressing major advances in knowledge and effective use of computers in a variety of application areas. The 78 papers presented in the AC 2015 proceedings address the following major topics: cognitive performance and work load, BCI and operational neuroscience, cognition, perception and emotion measurement, adaptive and tutoring training, applications of augmented cognition.