This review summarizes the health aspects of the medically important fungal genus Aspergillus. The morphology and systematics of the genus are explained as well as its biogeography. Major mycotoxins, the aspergilli that produce them, affected crops, and symptoms of the toxicoses are summarized, as are the major mycoses caused by aspergilli. The current status of the relationship between Aspergillus in the indoor environment and health issues are discussed.