PCR (polymerase chain reaction) is a technique used to amplify a single copy of DNA into many copies. It was developed in 1983 by Kary Mullis and has many applications in medical research. PCR works by using DNA polymerase to replicate a target piece of DNA through repeated heating and cooling cycles. Each cycle doubles the number of DNA copies. The process results in exponential amplification of the DNA target. PCR requires a DNA template, primers, DNA polymerase, nucleotides, buffer solution, and magnesium ions. It involves cycles of denaturation to separate DNA strands, annealing of primers to the template, and extension of new strands by the polymerase.