In the relatively short period since Cryptosporidium was recognised as a human pathogen, and that it could be transmitted in water as well as directly between animals and people, it has been the subject of intense investigations. Its status as an opportunistic pathogen, especially in AIDS patients, and the lack of effective anti-cryptosporidial drugs have served to emphasise the public health importance of this organism. This has to some extent overshadowed the fact that Cryptosporidium is also an important pathogen of domestic animals and wildlife. In recent years, the application of molecular biology and culture techniques have had an enormous impact on our understanding of the aetiological agents of cryptosporidial infections and our ability to study the causative agents in the laboratory. As a consequence, a wealth of information and novel data has been produced during the last 3-4 years, particularly in the areas of taxonomy, biology, pathogenesis, epidemiology - particularly zoonotic and water borne transmission, and treatment. It is thus very timely to bring together in this book the international research community involved to review the major advances in research and identify the important research priorities for the future, thus enabling as wide an audience as possible to benefit from and share in this comprehensive look at Cryptosporidium and cryptosporidiosis.