The sources used in this review were procured using Google Scholar. Keywords such as “polymerase chain reaction”, “polymerase chain reaction applications”, “polymerase chain reaction history”, “real time polymerase chain reaction”, and "digital polymerase chain reaction" were used when searching for sources present in this review. Sources which highlighted the invention of the PCR process were published from 1990 to present. Sources which highlighted today’s applications of PCR were published from 2015 to present. Sources which highlighted the real time and digital PCR processes were published from 2015 to present.