Adverse possession—sometimes called squatter's rights—occurs when a person or entity who does not own a certain piece of real property occupies or uses it in a way that is adverse to the owner of the property—meaning the use is in conflict or at odds with the property owner’s interests.

If this adverse possession or use of the property meets the legal standard for adverse possession—often described as use that is continuous, exclusive, hostile, open, and notorious—and continues for the prescribed period of time (usually specified in the state statute)—the person or entity adversely possessing or using the property will acquire ownership of the property (title). This ownership will result in the changing of boundary lines.

Because the required adverse possession must be open, obvious, and adverse to the owner’s interests, title may only be acquired by adverse possession to the portion of property that is used in that way.

Adverse possession laws vary from state to state and may be located in a state’s court opinions (also known as common law or case law) or, more often, in its statutes.

In Pennsylvania, adverse possession laws allow a person to claim ownership of a property if they have occupied it in a manner that is hostile, actual, visible, exclusive, and continuous for a statutory period. The required period of possession in Pennsylvania is 21 years, as per 42 Pa. Cons. Stat. § 5530. The occupation must be such that it gives the true owner a cause of action for ejectment. This means the possessor must treat the property as their own, without permission from the owner, and their use of the property must be apparent and not secretive. If all legal requirements are met, the individual claiming adverse possession can file a lawsuit to obtain legal title to the property. It is important to note that adverse possession claims can be complex and fact-specific, and an attorney can provide guidance on the likelihood of success and the process involved in making such a claim.