**Abstract**

The order Diptera includes all true flies. Members of this order are the most ecologically diverse and probably have a greater economic impact on humans than any other group of insects. The application of explicit methods of phylogenetic and morphological analysis has revealed weaknesses in the traditional classification of dipteran insects, but little progress has been made to achieve a robust, stable classification that reflects evolutionary relationships and morphological adaptations for a more precise understanding of their developmental biology and behavioral ecology. The current status of Diptera phylogenetics is reviewed in this chapter. Also, key aspects of the morphology of the different life stages of the flies, particularly characters useful for taxonomic purposes and for an understanding of the group's biology have been described with an emphasis on newer contributions and progress in understanding this important group of insects.

**Keywords:** Tephritoidea, Diptera flies, Nematocera, Brachycera metamorphosis, larva
