The great dream of philosophers and scientists has been to give a complete account of the order of things. The articulation of such a dream in the 20th century has been expressed in the idea of a unity of science. John Dupre systematically attacks the idea of scientific unity by showing how its underlying assumptions are at odds with the basic conclusions of science itself. In its stead, the author gives us a metaphysical interpretation much more in keeping with what science tells us about the world. The order presupposed by scientific unity is expressed in the classical philosophical doctrines of essentialism, materialist reductionism, and determinism. Employing examples from biology, that most "disordered" of sciences, Dupre subjects each of these doctrines to detailed and devastating criticism. He also identifies the shortcomings of contemporary approaches to scientific disunity, such as constructivism and extreme empiricism. He argues that we should adopt a "moderate realism" consistent with pluralistic science. Dupre's proposal for a "promiscuous realism" acknowledges the existence of a fundamentally disordered world, in which different projects or perspectives may reveal distinct, somewhat isolated, but nevertheless perfectly real, domains of partial order. This argument makes connections with discussions of science and value, especially in the work of feminist scholars. In Dupre's view, we have a great deal of choice about which scientific projects to pursue, a choice that can be informed only by value judgements. Such choices determine not only what kinds of order we observe in nature, but also what kinds of order we impose on the world we observe.