In this chapter I shall outline the methodology of instrumentalism, evaluate it and consider how it relates to methodological discussions within economics, and this will entail some consideration of Milton Friedman's famous, and controversial, essay on economic methodology. Discussion of this essay has been postponed until this chapter for two reasons. Firstly, Friedman's essay is increasingly being interpreted as owing more to instrumentalism than to the positivism implied in its title. Secondly, my earlier discussion of Popper helps to place instrumentalism into sharper relief. Friedman himself has claimed affinities with instrumentalism and Popper, but we shall see that these two perspectives are diametrically opposed. My consideration of instrumentalism will not be confined to Friedman's essay: a growing number of writers are suggesting that much contemporary econometric practice is essentially instrumentalist and I will consider such claims towards the end of the chapter.