In an economic model, an endogenous change is one that comes from inside the model and is explained by the model itself. For example, in the simple supply and demand model, suppose that there is a change in consumer tastes or preferences (an exogenous change). This leads to endogenous changes in demand and thus the equilibrium price and quantity.

In biological systems endogenous refers to something which is produced inside the organism or the cell.

See also: exogenous.