Interactivity refers to the exchange of commands and actions between a human (the user) and a digital creation. Interactive systems transform themselves according to the actions of the user. The simplest interaction might be implemented using a computer. With mouse movements and buttons clicks the user interacts with the computer.

More advanced forms of human computer interaction might involve changes inititiated by a users eye-movements, body movements and even physiological changes detected by EEG (Electroencephalography, detection of electrical brain activity from the scalp)