Fungi are a very diverse group of organisms and have a significant impact on the production, spoilage and safety of food. Molds have not only served to synthesize antibiotics but also to produce some foods. Fermented foods such as some cheese, soy sauce, miso, tempeh and other oriental delicacies are prepared with the help of molds.

It is well documented that some molds produce toxic substances. Amanita, a poisonous mushroom elaborates the toxin in macroscopic fruiting bodies. Some fungi always grow and sporulate as parasites on living host plants, and sometimes will do so only on a specific host. Claviceps is an example of this group of fungi and it produces mycotoxins. In contrast to fungi that are parasitic on living plants another group of fungi is saprophytic and causes destruction of dead plants and animal material. There is abundance of the spores of these molds in atmosphere and are found to inhabit stored grain and dried products and hence have been referred to as "storage fungi". These molds include Cladosporium, Fusarium, Penicillium, Aspergillus and Alternaria.