There have been noticeable changes in the epidemiology of many common sheep parasites over the past few years. It is not clear whether this reflects changes in sheep management and production and the sheep industry itself, the effects of climate change, the overuse of antiparasitics and selection for resistance (treatment practices and selection pressures), or, indeed, a function of all these factors. However, it is apparent that the implementation of parasitic control strategies needs to take these and other issues into account and, where necessary, such programmes will require appropriate modifications. This article discusses the affect of each factor and its impact on the prevalence of endo- and ectoparasitism in sheep.