© 2016 The AuthorsCryptosporidium is a ubiquitous enteric protozoan pathogen of vertebrates, and although recognised as a cause of disease in humans and domestic animals for over 50 years, fundamental questions concerning its biology and ecology have only recently been resolved. Overwhelming data now confirm that, like its close relatives, Cryptosporidium is a facultatively epicellular apicomplexan that is able to multiply in a host cell-free environment. These data must be considered in the context of the phylogenetic reclassification of Cryptosporidium from a coccidian to a gregarine. Together, they dictate an urgent need to reconsider the biology and behaviour of Cryptosporidium, and perhaps help to explain the parasite's incredible genetic diversity, distribution and host range. Improved imaging technologies have complemented phylogenetic studies in demonstrating the parasite's affinities with gregarine protozoa and have further supported its extracellular developmental capability and potential role as an environmental pathogen. These advances in our understanding of Cryptosporidium as a protozoan pathogen are examined with emphasis on how they may influence control strategies in the future.