Riparian habitats contain a rich diversity of organisms and serve as important linkages between freshwater and terrestrial ecosystems. Insects are a critical component of these ecosystems because of their numerical abundance, taxonomic diversity, and trophic significance. Aquatic insects are unique in that most species cross the interface and, thus, affect energy exchange between and within freshwater and terrestrial ecosystems. Unfortunately, our understanding of these processes, and of freshwater ecosystems in general, is stymied by the lack of data on ecosystem structure (i.e., biodiversity) and the lack of phylogenetic hypotheses through which these processes can be placed in a historical context. This is especially problematic for tropical faunas and certain taxonomic groups (e.g., Diptera). Our laboratory has been addressing these issues through studies of the structure and function of aquatic-insect communities, morphological and ecological adaptations of resident taxa, and potential mechanisms of reproductive isolation in aquatic insects. Much of this work has been international in scope, including projects in North America, Europe, Australasia (e.g., Australia & New Zealand), South Asia (e.g., Nepal). and Southeast Asia (especially Thailand). These projects are providing insights on not only the regional biodiversity, but on the biogeographic relationships between various faunas. Resultant data also have important implications for the use of aquatic insects as bioindicators of water quality and for the conservation of aquatic habitats.