In the philosophy of science, instrumentalism is the view that concepts and theories are merely useful instruments whose worth is measured not by whether the concepts and theories are true or false (or correctly depict reality), but by how effective they are in explaining and predicting phenomena.
Instrumentalism relates closely to pragmatism. This methodological viewpoint often contrasts with scientific realism, which defines theories as specially being more or less true. However, instrumentalism is more of a pragmatic approach to science, information and theories than an ontological statement. Often instrumentalists (just like pragmatists) have been accused of being relativists, even though many instrumentalists are also believers in sturdy objective realism (such as Karl Popper).