This chapter examines the salient literature on the immunology and pathology of members of the family Echinostomatidae in their definitive hosts, with emphasis on experimental studies that may provide useful information on factors that determine resistance to the parasites. For this purpose, several topics such as manifestations and mechanisms of resistance to infection, experimental strategies, and antigenic characterization of echinostomes are covered. Moreover, other topics such as immunodiagnosis are also analyzed. The analysis is focused on members of the genus Echinostoma . Although some of the nomenclature for echinostome species is disputed, the names used are those currently accepted. R. Toledo ( )