this book constitutes the refereed proceedings of the 5th international conference on augmented cognition, fac 2009, held in san diego, ca, usa in july 2009, within the framework of the 13th international conference on human-computer interaction, hcii 2009, with 9 other thematically similar conferences. the 94 revised papers presented were carefully reviewed and selected from numerous submissions. the papers are organized in topical parts on understanding human cognition and behaviour in complex tasks and environments, cognitive modelling, perception, emotion and interaction, cognitive load and performance, electroencephalography and brain activity measurement, physiological measuring, augmented cognition in training and education, brain-computer interfaces, and rehabilitation and cognitive aids.