A number of different uses of the concept true are distinguished within physics in order to answer the questions: When is a physical law true? and When is a theory true? It is shown that a law cannot be tested as true or false independently of some theory. The concepts of true in physics are shown to be quite different from those of philosophy. The uses of true in physics make no reference to nature or the external world as is often held, nor do the changes in theories bring us progressively nearer to a correct picture of nature.