A tangible user interface (TUI) is a user interface in which a person interacts with digital information through the physical environment. The initial name was Graspable User Interface, which is no longer used. The purpose of TUI development is to empower collaboration, learning, and design by giving physical forms to digital information, thus taking advantage of the human ability to grasp and manipulate physical objects and materials.

This was first conceived by Radia Perlman as a new programming language that would teach much younger children similar to Logo, but using special "keyboards" and input devices. Another pioneer in tangible user interfaces is Hiroshi Ishii, a professor at the MIT who heads the Tangible Media Group at the MIT Media Lab. His particular vision for tangible UIs, called Tangible Bits, is to give physical form to digital information, making bits directly manipulable and perceptible. Tangible bits pursues the seamless coupling between physical objects and virtual data.

There are several frameworks describing the key characteristics of tangible user interfaces. Brygg Ullmer and Hiroshi Ishii describe six characteristics concerning representation and control:

Eva Hornecker and Jacob Buur describe a structured framework with four themes:

According to Mi Jeong Kim and Mary Lou Maher, the five basic defining properties of tangible user interfaces are as follows:

A tangible user interface must be differentiated from a graphical user interface (GUI). A GUI exists only in the digital world, whereas a TUI connects the digital with the physical world. For example, a screen displays the digital information, whereas a mouse allows us to directly interact with this digital information. A tangible user interface represents the input directly in the physical world, and makes the digital information directly graspable.

A tangible user interface is usually built for one specific target group, because of the low range of possible application areas. Therefore, the design of the interface must be developed together with the target group to ensure a good user experience.

In comparison with a TUI, a GUI has a wide range of usages in one interface. Because of that it targets a large group of possible users.