A food chain is a linear network of links in a food web, often beginning with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as earthworms and woodlice), or decomposer (such as fungi or bacteria). A food web is distinct from a food chain. A food chain illustrates the associations between organisms according to the energy sources they consume in trophic levels, and the most common way to quantify them is in length: the number of links between a trophic consumer and the base of the chain.

Studies of food chains are essential to many biological studies.

Stability of the food chain is crucial for survival of most species. Removing even one component from the food chain could result in extinction or significant decreases in a species' probability of surviving. Many food chains and food webs contain a keystone species, a species that could directly affect the food chain and has a significant impact on the environment. The absence of a keystone species could destroy the balance of the entire food chain.

The efficiency of a food chain depends on the energy first consumed by the primary producers. This energy then moves through the trophic levels.

Food chains were first discussed by al-Jahiz, a 10th century Arab philosopher. The modern concepts of food chains and food webs were introduced by Charles Elton.

A food chain differs from a food web as a food chain follows a direct linear pathway of consumption and energy transfer. Natural interconnections between food chains make a food web, which are non-linear and depict interconnecting pathways of consumption and energy transfer.^{[citation needed]}

Food chain models typically predict that communities are controlled by predators at the top and plants (autotrophs or producers) at the bottom.

Thus, the foundation of the food chain typically consists of primary producers. Primary producers, or autotrophs, utilize energy derived from either sunlight or inorganic chemical compounds to create complex organic compounds, such as starch, for energy. Because the sun's light is necessary for photosynthesis, most life could not exist if the sun disappeared. Even so, it has recently been discovered that there are some forms of life, chemotrophs, that appear to gain all their metabolic energy from chemosynthesis driven by hydrothermal vents, thus showing that some life may not require solar energy to thrive. Chemosynthetic bacteria and archaea use hydrogen sulfide and methane from hydrothermal vents and cold seeps as an energy source (just as plants use sunlight) to produce carbohydrates; they form the base of the food chain in regions with little to no sunlight. Regardless of where the energy is obtained, a species that produces its own energy lies at the base of the food chain model, and is a critically important part of an ecosystem.