In anatomy, the cortex is the superficial layer of an organ. Included are such organs as the kidney, adrenal gland, ovary, thymus gland, and brain. Among these examples the cerebral cortex of the brain is the most familiar. The term designates no common characteristic of origin or structure, but only the existence of a distinctive layer at the surface of the organ involved.

In botany, the cortex is the outer portion of a stem or root, bounded externally by the epidermis, and internally by the cells of the pericycle. The cortex is composed mostly of cells which are very little differentiated. Usually these are rather large, thin walled parenchyma cells. The outer cortical cells often acquire irregularly thickened cell walls. These are the collenchyma cells. Some of the outer cortex cells may contains chloroplasts and carry on photosynthesis.