This paper presents a perspective on the ecology of trematodes in snail hosts based on recent evidence. Because flukes use snails almost obligatorily as first intermediate hosts, we highlight the role of gastropods as keystone species for trematodes and their communities. After reviewing recent developments in the transmission of trematodes to and from snails, we discuss trematode communities within individual snails (infracommunities) and in snail populations (component communities). Results garnered using various protocols at the infracommunity level are reviewed. The few data available, all from marine systems, indicate that low colonization rates characterize infracommunities, suggesting that trematode infracommunities tend to be isolationist in character rather than interactive. The variety of trematode species present in a component community seems to be determined by spatial overlap of definitive hosts. Relative abundance of species in a component community shows little dependence on negative interspecific interactions at the level of the infracommunity. Temporal aspects of trematode communities are related to the life history of the host snail. The component communities of long-lived snails (mostly marine) integrate many infection episodes whereas shorter-lived snails (mostly freshwater) acquire new component communities each time host cohorts turnover.