**Abstract**

*Cryptosporidium* species are protozoan parasites that infect epithelium surfaces in gastrointestinal and respiratory tracts of humans and a range of animals worldwide. Cryptosporidiosis has been associated with considerable morbidity and, under certain circumstances, mortality. Humans can acquire it by consuming food and drink containing oocysts, which have been recognised as a major cause for diarrhoeal disease. The ubiquitousness of the infective oocyst, its resilience to environmental pressures, and the low dose of oocyst exposure needed for infection amplify to outbreaks of *Cryptosporidium* traced to drinking and recreational water. Unlike in developing countries where lack of sustained access to safe water creates tremendous burdens of *Cryptosporidium* diarrhoea, this scenario is aggravated due to limited diagnosis and therapeutics. However, over the past few decades, growing information on *Cryptosporidium* genomes have allowed novel insight into the hostparasite relationship. Future field research on potential tools will focus on biologyderived parasite products applicable to drugs and diagnosis. This chapter reviews available data on biology, transmission, life cycle, diagnosis, genome, and a few but important progresses in the field of cryptosporidiosis.

**Keywords:** cryptosporidiosis, diagnosis, transmission, infectious disease, genome
