Legal Definitions - ancient-windows doctrine

The ancient-windows doctrine, also known as the ancient-lights doctrine, is a common-law principle that allows a landowner to acquire an easement preventing a neighbor from building an obstruction that blocks light from passing through the landowner's window after 20 years of uninterrupted use. The window or other opening is called an ancient light.

For example, if a landowner has had a window that has been receiving sunlight for 20 years, they can claim an easement to prevent their neighbor from building anything that would block the sunlight from passing through the window.

This doctrine has rarely been applied in the United States, and it has been repudiated in some states. However, it is still recognized in some countries, such as England.

Overall, the ancient-windows doctrine is a legal principle that protects a landowner's right to receive a reasonable amount of light, free from interruption, over adjoining land.