“Adverse possession” is a legal term that many of you may have heard. Most people probably don’t know what it means, however. Even most lawyers probably don’t really understand how it works. Simply put, adverse possession is a way that I can claim ownership of my neighbor’s land against my neighbor’s wishes.

I won’t try to go into how the legal principle of adverse possession came to be. It is very old. In order to understand how it works, however, you do need to know something about the logic behind it. Otherwise it will seem like nothing more than a way to steal your neighbor’s land. I think the real idea behind it is that if someone has been using a parcel of land for a long period of time, another person shouldn’t be able to claim it really belongs to him.

The principle is probably most easily understood in the context of owners of adjoining parcels of land. Let’s say you own the parcel of land next to mine. I believe the boundary between our respective parcels is in one place. You believe it is in a different place. I build a fence where I believe the boundary to be, which results in some land that is really yours being on my side of the fence. You don’t do anything about the fence being in the wrong place, and I use the land on my side of the fence, for ten years after I build it. At the end of that ten years, the land on my side of the fence becomes mine by adverse possession.

Nothing happens automatically at the end of the ten year period to document my ownership of the land on my side of the fence. If I want to have such a document, I have to file a lawsuit against you and prove the facts necessary to my claim of adverse possession. If on the other hand you file a lawsuit against me to get the fence moved to the true boundary, I can prove the facts necessary for adverse possession and thereby establish ownership of the land on my side of the fence. Pretty neat, huh?

One big obstacle to gaining adverse possession is permission from the true owner. If you know that I put the fence on your side of the boundary and I am using your land, you can prevent me from claiming adverse possession by simply sending me a letter before ten years have passed that says you know I am using your land that is on my side of the fence, that I have your permission to use it, but that you reserve the right to revoke your permission at any time. If I am using the land only with your permission, I can never make a valid claim of adverse possession.

I have of course left out a lot of messy details that make the principle hard to apply, and which lead to a lot of misunderstanding of the principle among lawyers and others. It can apply not only to ownership of a parcel of land, but also to the right to use a parcel of land for access to other land. The legal lingo for that application of the principle is “prescriptive easement.” The application of the principle is always more complicated than it sounds, and frequently depends on proof of facts that may be disputed or events that happened a long time ago. It is not the preferred way to settle whether your fence is really on the boundary between your land and your neighbor’s.