In this overview of the molecular genetics of resistance, pesticides are regarded as one of the many environmental stresses against which insects must defend themselves to survive. Examined at the genetic level, pesticide resistance appears to be a preadapted response to stress and not due to novel mutations caused by pesticide exposure. The genetic mutations–gene amplification, altered gene regulation, structural alteration of a gene–which result in resistance are described and explained and a possible distribution mechanism of resistance genes is considered. Resistance mechanisms, their associated biological processes and the types of genetic mutations associated with each are detailed. Finally, the potential of molecular technology for the development of novel methods to detect and monitor for resistance is examined and compared to more traditional technology.