Thaumaleidae, commonly referred to as madicolous midges, are a small family of aquatic Diptera (true flies). The larvae are restricted in their habitat to thin films of vertically flowing water, such as the margins of waterfalls, rock face seeps and cascading mountain streams. The restricted larval habitat and inconspicuous adults have led to thaumaleids being uncommonly encountered, under-collected and thus, understudied. The monophyly of the family is well supported, but generic concepts and relationships have never been rigorously tested, no phylogenies have been published and the validity of several genera is questionable. The overarching goal of this research is to produce the first comprehensive phylogeny for Thaumaleidae to ascertain generic relationships and test current generic concepts. Additional goals include alpha taxonomy and diversity studies. A new genus from Brazil, Neothaumalea Pivar, Moulton and Sinclair, is described. This is the first thaumaleid known from Brazil and east of the Andes. The Chilean thaumaleid fauna is also revised, bringing the known South American fauna from six species to seventeen. In addition to new species descriptions, all available life stages for previously known Chilean species are redescribed and illustrated, and distribution maps and keys to adults are provided. New larval morphotypes for Niphta spp. Theischinger are described and phylogenetic relationships hypothesized. Finally, the first phylogeny depicting thaumaleid generic relationships is constructed. Nucleotide sequences from three nuclear genes (big zinc finger, molybdenum cofactor sulfurase and elongation complex protein 1) were acquired from at least one representative of each genus and several outgroup taxa and analyzed with Bayesian methods. Results support the recognition of six genera within two clades: a Northern Hemisphere clade and a Southern Hemisphere clade. The Northern Hemisphere clade includes Trichothaumalea Edwards as sister to Thaumalea Ruthe (expanded to include Androprosopa Mik and Protothaumalea Vaillant). The Southern Hemisphere clade includes Afrothaumalea Stuckenberg as sister to Austrothaumalea Tonnoir (expanded to include Oterere McLellan) + (Neothaumalea + Niphta). This first comprehensive phylogeny for Thaumaleidae establishes a predictive framework with which to erect a stable classification and test myriad evolutionary hypotheses.