Low temperature physics is, almost by definition, that physical regime in which the complicating effects of the noise which is ubiquitous at room temperature has disappeared. How can we exploit this fact to answer questions of more general interest? In the first place, we can attempt to test some basic notions of quantum mechanics, e.g. the applicability of the theory to “macroscopic” collective variables, or the idea that “relative phase” is not defined until it is measured. Secondly, we can use the strongly cooperative tendency of many low-temperature systems, in particular those subject to some form of Bose condensation, to amplify small effects which may be unobservable, or very difficult to observe, at the level of a single particle. Thirdly, we can use low-temperature systems, which often have an extreme degree of purity and freedom from pre-existing defects, to test general notions about e.g. the mechanism of first-order phase transitions. I will discuss these and other possibilities, with particular emphasis on experiments in superfluid3He-B and the BEC alkali gases which have either recently been done or may be possible in the future.