The concept of producing multiple copies of a specific DNA molecule by a cycling process using DNA polymerase and oligonucleotide primers was first expounded in 1971 (Kleppe et al. 1971. J. Mol. Biol. 56: 341-361). The practical exploitation of such a process was hindered by the difficulty and cost of producing oligonucleotides, the non-availability of thermostable DNA polymerases and the lack of automated thermocycling instruments.

By the time of the first demonstration of the PCR process in 1985 (Saiki et al. 1985. Science 230: 1350-1354) automated oligonucleotide synthesizers were commonly available. The potential of PCR in a wide range of applications was recognised. It was still necessary to inject fresh thermo-labile polymerase prior to each elongation step and thermal cyclers were still in development.

The key step in realizing the potential of the PCR was the use of a thermostable polymerase which was first described in 1988 (Saiki et al. 1988. Science 239: 487-491). Since the first description of a practical DNA amplification process many refinements have been described and automatic thermal cyclers have become standard laboratory equipment.

PCR is now an essential tool for many biologists and the standard protocols are simple and user friendly. The exponential amplification process provides nanogram quantities of essentially identical DNA molecules starting from a few copies of a target sequence. The amplified material (the PCR amplicon) is available in sufficient quantity to be identified by size analysis, sequencing, amplicon melting or by probe hybridization. It can also be cloned readily or used as a reagent.