The objectives of dissertation work were to provide better taxonomic resolution for the true crane flies (Tipuloidea) by conducting a systematic investigation at multiple taxonomic levels (family, genus, and species). Representing the most taxonomically diverse group of flies (Insecta: Diptera), the Tipuloidea consist of over 15,000 described species, but present a difficult taxonomic structure with unavailable or inadequate taxonomic resources. The evolutionary relationships of this group were examined at multiple taxonomic levels in order to produce a classification and will provide a stable system by which the phylogeny, ecology, and biogeography was examined. The first quantitative analyses of the true crane flies are presented based on combined adult and immature morphological characters and DNA sequence data from the 28S ribosomal gene. Parsimony and Bayesian analyses using individual morphological and molecular datasets resulted in unresolved topologies. Greater resolution and tree support was obtained when both datasets were combined in both total evidence parsimony and Bayesian analyses than when analyzed separately. A revised classification is given for the true crane flies based on the results of these analyses. This revised classification further examines the newly defined subfamily Limoniinae through by providing diagnoses of all valid taxonomic units.;The revised taxonomic structure of the Limoniinae is used for an investigation of the crane flies of Thailand. Limoniinae flies were sampled at national parks across central to northern Thailand to observe patterns of species richness and turnover in this southeast Asian biodiversity hotspot. Sixty-six morphospecies from 28 genera were collected, with mountainous northern Thailand projected to have the highest diversity. The fauna of Thailand was stratified between the north and the south, with the north generally composed of more typically temperate genera and the south composed of more tropical genera. The increased diversity in northern Thailand was influenced by topology, with faunal assemblages changing across the latitudinal gradient of the north and providing more similar faunas at elevation between mountain ranges than within national park regions.;To investigate the species level diversity of the group the life history, morphological attributes, and phylogenetic relationships of the genus Lipsothrix Loew are evaluated. The revised genus contains 31 valid species, including one new species description for L. nullusarma from India. European and North America species have broad geographic distributions while species outside of Europe and North American are poorly collected and represented in collections by few specimens. The phylogenetic analysis recovered three major monophyletic groups, the basal Oriental assamica clade, a Western Palearctic nobilis clade, and a Western Palearctic and Nearctic clade (WP+N). The WP+N clade indicates that there has been significant faunal exchange between the two biogeographic regions and is hypothesized that exchange across the trans Beringian land bridge has occurred more than once.;Within the Tipuloidea, the high level of knowledge pertaining to the abundant species diversity acts to mask the underlying deficiencies in classification, phylogeny, and natural history. The lack of readily available taxonomic tools further reduces the knowledge of this group to little more than historic records within catalogs. This dissertation approached these systematic deficiencies at multiple taxonomic levels in order to address these issues and provide the groundwork for future studies.