Tangible User Interfaces (TUIs) have emerged as a new interface type that interlinks the digital and physical worlds. Drawing upon users' knowledge and skills of interaction with the real nondigital world, TUIs show a potential to enhance the way in which people interact with and leverage digital information. However, TUI research is still in its infancy and extensive research is required in order to fully understand the implications of tangible user interfaces, to develop technologies that further bridge the digital and the physical, and to guide TUI design with empirical knowledge.Tangible User Interfaces: Past, Present, and Future Directions surveys this rich and diverse field of research. It evaluates the existing body of knowledge with respect to designing, implementing, and evaluating TUIs, highlighting perspectives from human-computer interaction, design, engineering, psychology, and cognitive sciences. It concludes with a discussion on the strengths and limitations of TUIs and charts directions for future research.