An herbivore (from Latin herba = grass, vorare = to devour) is an animal that obtains its nutrition by consuming plants and algae, the primary producers (autotrophs). Since these consumers do not eat meat, one can think of herbivores as vegetarians. Examples of herbivores are cows and horses which eat grasses, hay, and other plants; caterpillars, which consume leaves; and marine zooplankton, which consume phytoplankton. Each ecosystem has its own specific set of herbivores, and within each ecosystem there are often several different types of herbivores, each eating a different type of producer. For example, in a rainforest, one herbivore might eat only a certain type of leaves, while another eats only specific fruit, and a third eats only nuts. Yet another herbivore might eat all three.

Because herbivores are not able to make their own food, they are considered heterotrophs. They must obtain all nutrients and energy from the food they consume.

Herbivores are a very important link in food webs. While they do not make their own food, they do pass energy and nutrients along the food web between producers and higher order consumers (the carnivores), thus linking these two levels. Because they are the first level of consumers in a food web, herbivores are often called primary or first-order consumers.