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 Maryland, adverse possession laws require that the possession of the property be continuous, exclusive, hostile, open, and notorious for a statutory period of 20 years. This means that the individual claiming adverse possession must use the property as a true owner would for two decades without interruption and in a manner that is visible and obvious to the actual owner. The use must also be without the permission of the owner, hence 'hostile.' If all legal criteria are met, the individual may be able to acquire legal title to the property. It's important to note that adverse possession claims can be complex and typically require the involvement of an attorney to navigate the legal process. Additionally, the actual owner may take legal action to prevent the loss of property through adverse possession, such as by challenging the claim in court or by interrupting the continuity of the adverse possessor's use.