Mycotoxins are toxic secondary metabolites produced by fungi that can contaminate food or feed. They are chemically stable and can be present in food commodities even if the fungi producing them have disappeared. Humans and animals may be exposed through the consumption of contaminated food or feed. There is a great variety of possible toxic effects that can be produced by these mycotoxins after acute or chronic exposure and maximum permitted levels have been established for some of them. Research to characterize their toxicity and to determine their presence in food is needed in order to preserve human health.