This chapter introduces the insect order Odonata. It provides the most recent phylogeny and up-to-date systematics as well as genera and species numbers of the various families in the biogeographic regions. We also present an overview about the general biology, ecology and behavior of Odonata. This includes details on morphology and ultrastructures. We also attempt an updated categorization of odonate life cycle types. The subchapters on ecology and behavior focus on various aspects of habitat selection and microhabitat occupancy, including effects of biotic interactions and antipredation behavior. Finally, we summarize collection and sampling methods for adult and larval Odonata. © 2015 Elsevier Inc. All rights reserved