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 Wisconsin, adverse possession laws are codified in state statutes, specifically under Wis. Stat. § 893.25 to § 893.33. To claim ownership of property through adverse possession in Wisconsin, the occupier must use the land continuously, exclusively, openly, and notoriously, and in a way that is adverse to the true owner's interests for a period of 20 years. The use must be such that it would give the owner a cause of action for trespass during this period. Additionally, the adverse possessor must pay property taxes on the land in question for the duration of the statutory period to strengthen their claim. If these conditions are met, the adverse possessor may be able to acquire legal title to the property, potentially resulting in changes to the boundary lines. It is important to note that adverse possession claims can be complex and contentious, often requiring the involvement of an attorney to navigate the legal process.