Feedback usually makes us think of those ear-splitting piercing tones that come across a PA system when it is being tested before a concert. Perhaps this is something that we would rather avoid having to experience, but this is only one aspect of feedback. Essentially, feedback is a situation created by a loop cycle, where output is fed back into the same system from which it first emerged. This could be a sound system, a visual system or even a mixture of the two. The common feature is the dynamic live quality of what is happening and the fact that there is a possibility of an artist being able to intervene in some way to influence the cycle. The arbitrary nature of feedback can be directed so that it partly conforms to a specific artistic intention. In the 1970s, Woody and Steina Vasulka’s work forged new sorts of relationships between the artist and technology. The Vasulkas’ systems were intricate and difficult to set up. In their case and those of others at the same time, the artist created not a final work but a situation of great creative possibility. Infinite variations were possible, depending on changes made to the systems’ settings on a moment by moment basis. There is now a raft of software environments that allow for the dynamic control and response to sound, video sensor data or MIDI. Some of these are commercial products such as Max/Msp/Jitter packages. Others are open source, such as Eyesweb, Pure Data and Processing.