Although we often think of fungi as organisms that cause disease and rot food, they are vitally important to human life on many levels. As we have seen, fungi influence the well-being of human populations on a large scale because they are part of the nutrient cycle in ecosystems. They have other ecosystem roles, as well. As animal pathogens, fungi help to control the population of damaging pests. These fungi are very specific to the insects they attack and do not infect animals or plants. Fungi are currently under investigation as potential microbial insecticides, with several already on the market.

The emerald ash borer (Agrilus planipennis) is an insect that attacks ash trees. It is in turn parasitized by a pathogenic fungus (Beauveria bassiana) that holds promise as a biological insecticide. The parasitic fungus appears as a white fuzz on the body of the insect. The mycorrhizal relationship between fungi and plant roots is essential for the productivity of farmland. Without the fungal partner in root systems, 80–90 percent of trees and grasses would not survive. Mycorrhizal fungal inoculants are available as soil amendments from gardening supply stores and are promoted by supporters of organic agriculture.

We also eat some types of fungi. Mushrooms figure prominently in the human diet. Morels, shiitake mushrooms, chanterelles, and truffles are considered delicacies The humble meadow mushroom, Agaricus campestris appears in many dishes. Moulds of the genus Penicillium ripen many kinds of cheese. They originate in the natural environment such as the caves of Roquefort, France, where wheels of sheep milk cheese are stacked in order to capture the moulds responsible for the blue veins and pungent taste of the cheese.