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 New York, adverse possession is governed by both statutory law and case law. The New York Real Property Actions and Proceedings Law (RPAPL) Section 501-525 outlines the requirements for a claim of adverse possession. To successfully claim adverse possession in New York, the occupant must demonstrate that their possession of the property was hostile, actual, open and notorious, exclusive, and continuous for a statutory period of ten years. The claimant must also pay taxes on the property during this period if the property is subject to taxation. Additionally, the law in New York has been amended to require that the claimant have a reasonable basis for believing that the land they possess is actually theirs, which is intended to prevent claims by intentional trespassers. If these conditions are met, the adverse possessor may be able to acquire legal title to the property, potentially resulting in changes to boundary lines. It is important for property owners to be aware of these laws to protect their property rights, and for potential adverse possessors to understand the strict requirements they must meet to claim ownership of property through adverse possession.