This chapter reviews research on understanding and controlling three of the most widespread and economically-relevant parasites of poultry and the infections they cause: Eimeria species (coccidiosis), Histomonas meleagridis (histomonosis) and Dermanyssus gallinae (the poultry red mite (PRM)). In each case the chapter reviews advances in areas such as: incidence and economic significance, host-pathogen interactions, population dynamics, detection, control and prevention as well as ongoing challenges in parasite management.