Polymerase refers to the category of enzymes which catalyze the synthesis of nucleic acid (DNA/RNA) by linking the monomer which in this case is nucleotides, the building blocks of nucleic acids. Depending upon the nucleic acid one is working with polymerase could be DNA or RNA specific. In PCR, a synthetic polymerase such as Taq polymerase is commonly used because of its heat resistant ability. Since Taq is active at room temperature as well it can result in non-specific amplification. In order to minimize this, a Hot start PCR polymerase is used which inactivates Taq at lower temperatures increasing the efficiency of PCR. Reverse transcriptase is another example of the naturally occurring polymerase. It exists in RNA retrovirus (like HIV for example) and synthesizes complementary strand to the preexisting strand of viral RNA. RNA-dependent RNA polymerase (also known as RNA replicase) catalyzes replication of RNA from RNA template. DNA dependent RNA polymerase, on the other hand, catalyzes the transcription of RNA from a DNA template. Another type is a Long-range PCR polymerase which can amplify longer than usual DNA length.

The polymerase is different for prokaryotic and eukaryotic systems. Polymerasesare valuable reagents and must be stored and handled with care.