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 Arizona, adverse possession is governed by state statutes, specifically under Arizona Revised Statutes Sections 12-521 to 12-528. To claim adverse possession in Arizona, the occupant must have possessed the property continuously for a statutory period, which is typically 10 years. The possession must be actual, open, notorious, exclusive, hostile, and under a claim of right. This means the occupant must treat the property as their own, without permission from the true owner, and their occupation must be obvious to anyone, including the owner. If all legal requirements are met, the adverse possessor can potentially acquire legal title to the property. It's important to note that adverse possession claims can be complex, and the specific facts of each case are critical. Therefore, anyone considering or contesting an adverse possession claim should consult with an attorney to understand their rights and obligations under Arizona law.