Adverse Possession
In real estate law, adverse possession is a means of acquiring title to someone else's real property without compensation.

Adverse possession requires the actual, hostile, notorious, visible, exclusive, and continuous possession of the property, and some jurisdictions further require that the possession be made under a claim of title. Simply, this means that those who are attempting to claim the property are occupying it exclusively (keeping out others) and openly as if it were their own property. Some jurisdictions permit accidental adverse possession as could occur with a surveying error. Generally, the openly hostile possession must be continuous (although not necessarily constant) without permission or challenge from the lawful owner, for a fixed statutory period in order to gain title. Where the property is of a type ordinarily only occupied during certain times (such as a summer cottage), the adverse possessor may only need to be in exclusive, open, hostile possession during those successive useful periods.

This is sometime called "squatters' rights". If the squatter abandons the property for a period, or if the rightful owner effectively removes the squatter's access even temporarily during the statutory time period, the "clock" usually starts running. However, one squatter may pass along continuous possession to another squatter, known as "tacking", until the adverse possession period is complete. A lawful owner may also restart the "clock" by giving temporary permission for the occupation of the property, thus defeating the necessary "continuous and hostile" element. Evidence that a "squatter" paid rent to the owner would defeat adverse possession for that period.

Once the statute of limitations has expired for evicting the trespassers, and assuming the legal owner has done nothing to halt the process, the successful adverse possessors acquire equitable title to the land, to the extent it was actually possessed (e.g., just the part they occupied, not necessarily everything on the legal owner's deed). At that point they no longer need to continuously, exclusively or openly occupy any part of the land because they now own it. However, to become the legal owners of record (helpful to have a deed for future transactions), they may bring an action in land court to "quiet title" of record in their names on the former owner's property.

Adverse possession does not typically work against property owned by a government agency. It also fails to give any rights if the land is registered under a Torrens title registration system.