For many bacterial pathogens, including Staphylococcus aureus, pulsed-field gel electrophoresis (PFGE) is a molecular typing method widely used in surveillance and epidemiological investigations. The general principle of PFGE involves creating large DNA fragments from intact bacterial chromosomes using rare cutting restriction endonucleases. These large DNA fragments are successfully separated in an agarose gel by alternating the direction of the electrical fields over a prolonged period of time. The resulting DNA banding patterns in the gel create a "DNA fingerprint," which can then be used to discriminate clonal relatedness of isolates based on set interpretation guidelines. Standardization of protocols has greatly enhanced the reproducibility of PFGE between labs, enabling national surveillance and further molecular epidemiological studies of S. aureus.