Endogeny, in biology, refers to the property of originating or developing from within an organism, tissue, or cell.

For example, endogenous substances, and endogenous processes are those that originate within a living system (e.g. an organism or a cell). For instance, estradiol is an endogenous estrogen hormone produced within the body, whereas ethinylestradiol is an exogenous synthetic estrogen, commonly used in birth control pills.

In contrast, exogenous substances and exogenous processes are those that originate from outside of an organism.