Limiting factors are variables or environmental conditions that restrict the growth, distribution, or abundance of an organism or population within an ecosystem. They can be biotic, such as food, mates, and competition with other organisms for resources, or abiotic, such as space, temperature, altitude, and amount of sunlight available in an environment. Some examples of limiting factors that could limit the size of a population are food, nutrients, shelter, and mate. Limiting factors can be single-limiting, when only one factor limits the system, or co-limiting, when a factor causes an indirect restrictive effect or increases the effect of a direct limiting factor.

The concept of limiting factors is based on Liebigs Law of the Minimum, which states that growth is controlled not by the total amount of resources available, but by the scarcest resource. Limiting factors are usually expressed as a lack of a particular resource. For example, if there are not enough prey animals in a forest to feed a large population of predators, then food becomes a limiting factor. Ultimately, limiting factors determine a habitats carrying capacity, which is the maximum size of the population it can support.