To accompany a new collection of methods and protocols, we discuss the relevance of the microbial eukaryotes belonging to the protist phylum Euglenozoa. For those interested by Euglena, applied biology is often relevant: as a starting point for useful natural products including biofuels, nutritional supplements, and metabolites with biomedical potential, or as an environmental agent for bioremediation. Arguably the most widely studied euglenozoans are the parasitic trypanosomatids. Collectively, trypanosomatids cause several serious neglected tropical diseases and economically important diseases of animals and plants; since the early 1900s, drug discovery and disease intervention have been prominent research areas. Yet for those interested in evolution, trypanosomatids and Euglena are host to all sorts of extreme biology either not seen or so pronounced in other eukaryotes. Euglenozoans are also relevant in an ecology context: free-living relatives of the trypanosomatids are abundant in freshwater environments. Moreover, the other major euglenozoan group, the diplonemids, are recently recognized as the most abundant heterotrophic protists in the world’s oceans, their diversity and abundance at least comparable to major algal groups. Finally, the long history of euglenozoan study illustrates nicely the evolving nature of scientific discovery and reporting since Van Leeuwenhoek first saw Euglena in the pioneering days of microscopy.