This selective review of 40 years of coccidiosis research is one of a number on important diseases of poultry to celebrate the 40th anniversary of the birth of Avian Pathology, the journal of the World Veterinary Poultry Association, and is written for the non-specialist. The intention is to provide a flavour of the field problems and intellectual challenges, with emphasis in the areas of immunology and vaccinology that drove research in the 1970s, and to reflect on research progress since.