Why study the development of insect nervous systems? Beyond satisfying sheer curiosity, knowledge of insect neural development holds the hope of revealing novel and specific paths for biologically sensitive intervention to protect or to control specific populations of insects. Furthermore, for developmental biologists, insects offer a rich source of material. The development of the nervous system in insects follows different paths, depending on the life history of the species, yet many of the cellular and molecular mechanisms underlying neural development appear to be common across disparate insect species, and even common between insects and mammals (see Arendt & Nubler-Jung 1999). Individual species variations confer particular experimental advantages to the investigator using insects. For all of these reasons, recent years have seen a huge research effort to understand neural development in insects. Unable to review all of insect nervous system development in a one-hour presentation, I will provide a very selective review. I will focus on the growing understanding of the importance and nature of cellular interactions in insect neural development. The nervous systems of certain insects have been excellent systems in which to study these interactions. Drosophila melanogaster, a superb organism for genetic studies, has been used to great advantage to reveal the cellular and molecular bases for developmental influences in the peripheral and central nervous systems. Large holometabolous insects, such as the hawkmoth Manduca sexta, have different advantages; for instance, developing sensory and central neural structures are readily accessible throughout a major postembryonic wave of development (during the metamorphosis of the larva to the adult), when the animal is large and hardy, readily amenable to surgical manipulations. Manduca, besides being useful for cellular studies, also has been especially useful for studies of the molecular bases of hormone action, a special type of long-range cellular interaction, in neural development (Levine et al. 1995). Insect nervous systems develop along widely differing timetables, depending on the life stages of the species. In this review, I will provide background on embryonic development and metamorphosis of the nervous system, but will focus mostly on intercellular interactions that play key roles no matter what the timetable, no matter what the extent of postembryonic reorganization, of the developing nervous system. I will go into most depth on intercellular interactions during development of the antennal system in Manduca.