Medicine is changing rapidly. In part, this is due to the accumulation of discoveries in biomedical science. However, this is not sufficient to explain the changes clinicians see. Whereas once medical advance concerned discoveries external to clinical practice (such as the identification of a causative microorganism or gene), medical practice itself is now a subject of study. What clinicians know, how they acquire knowledge, and how knowledge is distributed are all subjects of scrutiny. In short, medicine is being industrialized: we can see the twin changes of specialization, and the desire to codify practice such that those with different educational backgrounds can undertake a clinical role. Key to such change is the role played by evidence. Whereas once natural science was seen to determine clinical practice, this view is now known to be mistaken. How we can formally combine evidence from different traditions is, despite the claims of the evidence-based medicine movement, as yet unresolved.