The science of the so-called polymerase chain reaction (PCR) is now well known. However, the legal story associated with PCR is, for the most part, not understood and constantly changing. This presents diffculties for scientists, whether in academia or industry, who wish to practice the PCR process. This chapter summarizes the major issues related to obtaining rights to practice PCR. The complexity of the patent system is explained with a few PCR-specific examples highlighted. The chapter also provides an overview of the exemption or exception from patent infringement associated with certain bona-fide researchers and discusses the status of certain high-profle patents covering aspects of the PCR process.