Fungi are plant-like organisms that lack chlorophyll. Fungi are one of the five kingdoms of life. Many fungi are good and useful (edible mushrooms would be an example of these) while some cause problems (some fungi can injure plants and people). There are over 100,000 species of fungi. Mycologists are the scientists who study fungus.

Since they do not have chlorophyll, fungi must absorb food from others. Since they don't use light to make food, fungi can live in damp and dark places. Fungi are supposed to "eat" things when they are dead but sometimes they start eating when the organism is still alive. That is when mycologists come in to figure out what to give to the infected patient or plant to get rid of the fungus.

Fungi cause a wide variety of diseases in human. The most frequent cause of fungal infection of man are the various forms of candidiasis. Candida spp. can produce infections in both otherwise healthy individuals and in individuals with reduced immune system function.