While today's pervasive digital devices put the world’s information at our fingertips, they do not help us with some of the cognitive skills that are arguably more important to leading a successful life, such as motivation, attention, memory, creativity, and emotion regulation. Building upon insights from psychology and neuroscience, the Fluid Interfaces group creates systems and interfaces for cognitive enhancement. Our designs enhance cognitive skills by teaching users to exploit and develop the untapped powers of their mind and by seamlessly supplementing users' natural cognitive abilities. The solutions we design are compact and wearable to support real-life studies and interventions. Our work is highly interdisciplinary and combines insights and methods from human computer interaction, sensor technologies, machine learning, brain computer interfaces, psychology, and neuroscience to create new opportunities for studying and intervening in human psychology in-the-wild.