Ownership gained by possessing land long enough under conditions set by law.

"Possessing" means actual physical use or control of the property, not a casual trespass. "Long enough" means the full statutory period runs without interruption. "Under conditions set by law" means the possession must be open, visible, exclusive, and continuous, and it must conflict with the true owner's rights rather than exist with permission. In Wisconsin, the basic rule appears in Wis. Stat. § 893.25: 20 years of uninterrupted adverse possession can transfer title when the claim is not based on a written instrument. For claims founded on a recorded written instrument, Wis. Stat. § 893.26 sets a 10-year period. Wisconsin also requires actual occupation; under § 893.25(2), land is usually treated as occupied only if it is protected by a substantial enclosure or usually cultivated or improved.

The practical point is control. A successful adverse possession claim can change title, boundary lines, access rights, and who has legal responsibility for the land. That can affect a sale, a mortgage, or a quiet title action.

It can also affect an injury claim. If someone is hurt on disputed property, the real question may be who had possession and control at the time of the accident. That can change premises liability, insurance coverage, maintenance duties, and the identity of the proper defendant.