The strangely audacious notion that human sickness could be cured with concoctions made from natural products existed in most ancient civilisations. This fantastic dream began to come true in the twentieth century, as chemistry and pharmacology were harnessed to make reproducibly effective versions of folk medicines. Prospects for discovering useful drugs greatly improved with the discovery of the first antibiotics and the realisation that these were representatives of a chemical universe of hitherto unimagined richness containing molecules of extraordinary biological potency. With inspiration from nature and growing sophistication, synthetic chemists have learnt how to generate vast libraries of chemicals, which the drug discovery industry screens for useful medicines. We will consider the prospects of protein medicines in the following chapter.