Aspergilli are imperfect filamentous fungi belonging to the class Deuteromycetes. Some perfect forms (sexual) are known and belong to the class Ascomycetes (Emericella, Eurotium, Neosartorya, etc). About 200 species of Aspergillus are known, of which twenty are involved in human pathologies (A. carbonarius, A. flavus, A. fumigatus, A. ochraceus, A. parasiticus, etc.).

The colonies are powdery or downy, grow rapidly, and usually display various bright colors. The hyaline thallus has a compartmentalized mycelium bearing numerous erect conidiophores with a typical vesicular extremity called the "head of Aspergillus". The globular conidia, usually 2 to 3 μm in size, are produced from the phialides that are grouped at the top or all around the vesicles, with or without intermediate metula.

The Aspergilli are cosmopolitan. They are ubiquitous saprophytic molds (decomposing organic matter, soil, dust, compost, food, cereals ...). They are omnipresent in the human environment. Each head of Aspergillus is capable of producing up to 104 spores. The Aspergillus produce many mycotoxins (kojic acid, neoaspergillin acid, aflatoxins, griseofulvin, ochratoxin, sterigmatocystin, etc.) and are involved in many relatively severe diseases grouped under the term "aspergillosis".

Aspergilli are widely used in the food, chemical and biotechnological industries.

List of species