DNA-based procedures are becoming increasingly common within the analytical laboratory where the polymerase chain reaction (PCR) has become an indispensable technique. Developed in 1985 by Kary B. Mullis, PCR revolutionized the way that deoxyribonucleic acid (DNA) could be copied. Mullis's invention allowed researchers to make millions of copies of a selected DNA region within hours. Today, PCR can take minutes. PCR has widespread analytical applications in the food, environmental, medical and forensic fields. This Technical Brief covers the basics of PCR and some of its variations.