Caddisfly collections from 25 springs across Canada reveal some general trends and some regional and habitat-related differences in spring faunas. In general the number of caddisfly species present in springs increases with habitat diversity. Limnocrenes and rheocrenes with low current and small-sized substrate particles support few caddisfly species, but may have large populations of individual species. Species categorized as grazers, shredders, and predators are common in springs, but filter-feeders are rare.Eastern and western springs have many genera but few species in common. About 35% of the species recorded in this study are from the family Limnephilidae, but the most frequently encountered genus was Parapsyche (Hydropsychidae), usually P. apicalis (Banks) in the east and P. elsis Milne in the west (British Columbia and Alberta). Other common genera in both east and west were Neophylax, Lepidostoma, and Rhyacophila. Common genera collected only in the west were Anagapetus, Homophylax, Psychoglypha, and Neothremma, and Frenesia and Pseudostenophylax were taken only in the east. Three analytical techniques — ordination by detrended correspondence analysis, constrained ordination by canonical correspondence analysis, and classification by two-way indicator species analysis — all confirmed an east/west geographical difference in caddisfly communities and pointed to elevation, extent of groundwater source, and summer temperature as environmental factors influencing, but not totally responsible for, east/west species distributions. Past and present barriers to migration both appear to be important. Riparian vegetation, current, substrate particle size, microhabitat diversity, and pH all have strong influences upon the composition of spring communities in both the east and the west. Springs in which caddisflies were primarily associated with detrital processing were dominated by Frenesia and Lepidostoma in the east but by Homophylax in the west. Scrapers and predators were abundant only in springs with relatively high microhabitat diversity, current speed, and PH.