Dragonflies (Odonata) are a favorite organism for behavioral studies because they are common, diurnal and easy to observe. These studies are often difficult to interpret, however, because of a lack of phylogenetic consensus. Although several morphology-based phylogenetic hypotheses have been proposed, these phylogenies have been contradictory and uncorroborated. The research presented here examines the superfamily Libelluloidea. This superfamily includes the three most commonly encountered families (Corduliidae, Macromiidae and Libellulidae). It is unclear from previous morphological efforts whether these taxa comprise three distinct families or simply one family containing many subfamilies. Using the D2 and D7 portion of the large ribosomal subunit and a morphological data set I have constructed a preliminary phylogeny of 120 taxa. For this analysis I used outgroup taxa from the families Cordulegastridae and Petaluridae. I have aligned my data using ribosomal secondary structure alignment methods in an attempt to resolve the alignment problems with previous molecular studies . In addition to answering questions about the taxonomic status of these three families, this phylogeny provides insight into the behavioural traits of the Libelluloidea. Although preliminary, this phylogeny may reveal whether the loss of the ovipositor, found in the families Libellulidae and Gomphidae and often considered a shared derived character, is instead a convergent loss. This phylogeny may also determine whether their diversification immediately followed an increase in the cumulative larval niche space of these dragonflies (particularly the use of sediments for concealment) and whether their diversification, triggered by sexual selection, permitted the loss of the ovipositor.