The origin of flight in insects continues to excite speculation and debate. This chapter is concerned with genetic and environmental influences on insect flight. Genotype-environment interactions are also evident in strains of Drosophila which show differences in their responses to density and to the presence of “competitors” of sibling species, but the densities involved are high and the actual nature of the interactions is unknown. For several temperate and tropical species with a range of different habitat requirements, there is evidence of migratory behavior and of the genetic and environmental factors which regulate it. Evidence for genetic variation in the capacity for flight associated with foraging behavior is difficult to identify because it is often discussed loosely as migration or dispersal. Selection for rapid flight over a few centimeters, from holding to catching containers, by Anastrepha suspensa and Ceratitis capitata has been achieved and its slow progress and variation between generations indicates a polygenic effect.