This document provides an overview of polymerase chain reaction (PCR). It describes PCR as a method for amplifying a specific region of DNA through repeated cycles of heating and cooling. Each cycle doubles the amount of target DNA. The key components of PCR are template DNA, primers, DNA polymerase enzyme, and nucleotides. The document outlines the three stages of PCR - denaturation to separate DNA strands, annealing where primers attach to strands, and elongation where new strands are synthesized. Applications of PCR include genome mapping, disease diagnosis, and forensics.