The classification and evolutionary history of the superfamily Empidoidea (Diptera) have been far from straightforward subjects. Morphology based phylogenies of the superfamily have been unable to answer many questions raised by both systematists and biogeographers, as well as ecologists and ethologists, partly due to morphological modifications and adaptations difficult to interpret. In paper I a phylogeny is presented which was the first published that was based on molecular data with multiple loci and with high support. We sampled several groups never included in molecular analyses before and were able to resolve several relationships and recover several species groups that were previously unplaced. Atelestidae is confirmed as the sister group to remaining families. Hybotidae is sister group to Dolichopodidae, Ragadidae stat. n. and Empididae. Species included in the family Brachystomatidae are found to be nested within Empididae and Brachystomatidae is therefore lowered to subfamily. The erection of Ragadidae to family, sister to Empididae, is based on genetic distances between the present families and subfamilies. Paper II deals with the genus Wiedemannia (Empididae: Clinocerinae), also using molecular data but also put into a spatial and temporal context with molecular dating. The subgenera are found to be non-monophyletic and are therefore suggested to be rejected as accepted names. The dated tree, based on molecular data and known fossil records, suggests an initial diversification 50 million years ago followed by further diversification events that may be linked to changes in sea levels on a global scale. We also provide a Species Distribution Model map suggesting areas of potential hot spots as based on climatic variables. Following the results in paper I, the internal relationships of Ragadidae are revised in paper III. The lack of DNA data, partly caused by few available specimens and the rarity of some species, motivated a morphological approach together with a maximum parsimony analysis to investigate the monophyly of species groups and genera. The flower feeding genera Iteaphila and Anthepiscopus are found to form a distinct monophyletic clade together with Hormopeza. The internal relationships are revised, updated diagnostic characters are provided as well as a determination key to the genera. In paper IV we deal with the taxonomical issue of Chvalaea sopianae and C. rugosiventris, two species in the family Hybotidae. Both species were originally described from single female specimens.  However, the sex of C. rugosiventris was mistaken in the original description, and the differential characters of the two species are based on sexual dimorphism. The two species are synonymized and the male of C. rugosiventris redescribed. We also provide additional geographic data on the hybotid species Allanthalia pallida and Leptodromiella crassiseta. The final paper, paper V, presents records of new species to Sweden and new records within Sweden of a large number of species of Hybotidae, Empididae and Ragadidae. We also provide a substantial addition of genetic barcodes of the Swedish fauna, shared publicly in The Barcode of Life Database. This increases the coverage of Swedish taxa in the database with 71% for Empididae and 13% for Hybotidae.