Possession is nine-tenths of the law is an expression meaning that ownership is easier to maintain if one has possession of something, or difficult to enforce if one does not. The expression is also stated as “possession is nine points of the law”, which is credited as derived from the Scottish expression “possession is eleven points in the law, and they say there are but twelve.”

Although the principle is an oversimplification, it can be restated as: “In a property dispute (whether real or personal), in the absence of clear and compelling testimony or documentation to the contrary, the person in actual, custodial possession of the property is presumed to be the rightful owner. The rightful owner shall have their possession returned to them; if taken or used. The shirt or blouse you are currently wearing is presumed to be yours, unless someone can prove that it is not.”

The adage is not literally true, that by law the person in possession is presumed to have a nine times stronger claim than anyone else, but that “it places in a strong light the legal truth that every claimant must succeed by the strength of his own title, and not by the weakness of his antagonist’s.”[ The principle bears some similarity to uti possidetis (“as you possess, so may you continue to possess”), which currently refers to the doctrine that colonial administrative boundaries become international boundaries when a political subdivision or colony achieves independence. Under Roman law, it was an interdictum ordering the parties to maintain possession of property until it was determined who owned the property.

In the Hatfield-McCoy feud, with testimony evenly divided, the doctrine that possession is nine-tenths of the law caused Floyd Hatfield to retain possession of the pig that the McCoys claimed was their property. It has been argued that in some situations, possession is ten-tenths of the law. While the concept is older, the phrase “Possession is nine-tenths of the law” is often claimed to date from the 16th century. In some countries, possession is not nine-tenths of the law, but rather the onus is on the possessor to substantiate his ownership.

This concept has been applied to both tangible and intangible products. In particular, “knowledge management” presents problems with regard to this principle. Google’s possession of a large amount of content has been the cause of some wariness due to this principle. It has been said that there was a time in which the attitude towards rights over genetic resources was that possession is nine tenths of the law, and for the other tenth reliance could be made on the principle that biological resources were the heritage of mankind.

Aboriginal people frequently encounter this principle. There is some question as to whether the principle applies to Native American land claims. It has been said that “squatter’s rights” and “possession is 9/10ths of the law” were largely responsible for how the American west was really won.

Walter Block has stated, “Suppose that 100 slaves worked on the plantation, but only one heir of any of them, B, can now be found. Does B get the entire value of the landed estate (apart from the house), or only one percent of it. The answer is the latter. For possession is 9/10ths of the law. He who is the present land holder (W in our case) is always deemed to be the proper owner, unless evidence to the contrary can be adduced. But the claim of B, stemming from the work of his grandfather, B, can at most encompass what he, B, that is, contributed to the enhancement of the value of the property. The other ninety-nine percent of the value of this land will remain with W, until and unless other grandchildren of slaves come forth with proof of parentage.”

Murray Rothbard noted that libertarians “conclude that even though the property was originally stolen, that if the victim or his heirs cannot be found, and if the current possessor was not the actual criminal who stole the property, then title to that property belongs properly, justly, and ethically to its current possessor.”