Climate change has become a huge threat to terrestrial and aquatic ecosystems globally. While most attention has been focused on potential effects on free-living organisms, there also has been widespread interest on effects on pathogens and disease. Parasites will no doubt be impacted by climate change, but whether they increase or decrease in abundance, or increase or decrease their distribution, is not obvious. Because transmission of parasites is linked to abundance and diversity of potential hosts, climate change effects on free-living organisms will also affect their parasites. Herein, advances in effects of increasing temperature on parasites and host–parasite interactions are explored, with emphasis on recent advances in acclimation effects and the application of metabolic models to particular host–parasite systems. Climate change will also affect the immune function and physiology of aquatic organisms. Furthermore, climate change does not operate in a vacuum, and there are numerous associated abiotic effects that will impact parasites and their hosts. Effects of precipitation and drought, hydrological changes, eutrophication, acidification, salinity and contaminants in relation to a warming climate are examined for parasites of freshwater and marine ecosystems. Nor do these effects operate independently, and combined effects of multiple stressors on host–parasite systems are discussed. This chapter concludes with an examination of higher order ecological effects and ecosystem consequences of parasitism in a warming climate, and finally, a series of case studies on effects of climate change on particularly well-studied aquatic parasites.