Lost, mislaid, and abandoned property are categories of the common law of property which deals with personal property or chattel which has left the possession of its rightful owner without having directly entered the possession of another person. Property can be considered lost, mislaid, or abandoned depending on the circumstances under which it is found by the next party who obtains its possession.

An old saying is that possession is nine-tenths of the law, dating back centuries. This means that in most cases, the possessor of a piece of property is its rightful owner without evidence to the contrary. More colloquially, these may be called finders, keepers. The contradiction to this principle is theft by finding, which may occur if conversion occurs after finding someone else's property.

The rights of a finder of such property are determined in part by the status in which it is found. Because these classifications have developed under the common law of England, they turn on nuanced distinctions. The general rule attaching to the three types of property may be summarized as: A finder of property acquires no rights in mislaid property, is entitled to possession of lost property against everyone except the true owner, and is entitled to keep abandoned property. This rule varies by jurisdiction.