SynopsisEvaluation of the potential response of parasites of aquatic organisms to climate change illustrates the complexity of host-parasite relationships and the difficulty of making accurate predictions for these biological systems. In recent years, trematodes have proven to be a useful model to evaluate potential effects of climate change on host-parasite systems. In the first part of this article, I review and summarize results from the recent use of trematodes and specifically their early life cycle stages in testing effects of temperature and other climate-driven variables on life history traits and host-parasite interactions. However, metazoan parasites in aquatic systems respond directly to changes in temperature and also to changes in other climate-driven abiotic parameters that are mediated directly on the parasite or indirectly through changes in the distribution and abundance of their hosts. In addition, though most research to date has focused on the effects of temperature, it is imperative to explore effects of precipitation, eutrophication, acidification, water levels and flow rates, habitat loss and fragmentation, extreme weather, and other forms of anthropogenic interference on the distribution of both hosts and parasites, as these biotic and abiotic factors and stressors do not operate independently of climate. In the second part of this article, the effects of some of these factors derived from our own field studies, as well as other investigations both in the laboratory and the field, on the distribution, abundance, and community structure of parasites in aquatic ecosystems will be reviewed and discussed.