Technical Abstract: Genetic transformation of insect species can be achieved by transient or somatic expression of DNA, or by the heritable expression of genes integrated into chromosomes. Stable germ-line transformation is now possible with several transposable element systems, and has succeeded in nearly 20 species within four orders of insects. For some of these species, transformation can now be considered routine. Other vector systems include viruses and bacterial symbionts that have demonstrated utility in species and applications requiring transient expression, and for some, the potential exists for genomic integration. These findings present a dramatic turning point in our ability to study and manipulate agriculturally and medically important insects. Importantly, it will now allow the creation of transformed strains for basic studies to understand insect biology, especially functional genomics analysis, and the development of strains useful for improved and efficient biocontrol strategies. The practical use of transformed insects in field release programs will require continued modifications and analysis to ensure transgene stability.