The development of the polymerase chain reaction (PCR) has often been likened to the development of the Internet, and although this does risk overstating the impact of PCR outside the scientific community, the comparison works well on a number of levels. Both inventions have emerged in the last 20 years to the point where it is difficult to imagine life without them. Both have grown far beyond the confines of their original simple design and have created opportunities unimaginable before their invention. Both have also spawned a whole new vocabulary and professionals literate in that vocabulary. It is hard to believe that the technique that formed the cornerstone of the human genome project and is fundamental to many molecular biology laboratory protocols was discovered only 20 years ago. For many, the history and some of the enduring controversies are unknown yet, as with the discovery of the structure of DNA in the 1950s, the discovery of PCR is the subject of claim and counterclaim that has yet to be fully resolved. The key stages are reviewed here in brief for those for whom both the history and application of science holds interest.