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 …