In law, a lien is a form of security interest granted over an item of property to secure the payment of a debt or performance of some other obligation. The owner of the property, who grants the lien, is referred to as the lienor and the person who has the benefit of the lien is referred to as the lienee.

The etymological root is: Anglo-French lien, loyen bond, restraint, from Latin ligamen, from ligare to bind.

In the United States, the term lien generally refers to a wide range of encumbrances and would include other forms of mortgage or charge. In the U.S., a lien characteristically refers to non-possessory security interests (see generally: Security interest - categories).

In other common law countries, the term lien refers to a very specific type of security interest, being a passive right to retain (but not sell) property until the debt or other obligation is discharged. In contrast to the usage of the term in the U.S., in other countries it refers to a purely possessory form of security interest; indeed, when possession of the property is lost, the lien is released. However, common law countries also recognize a slightly anomalous form of security interest called an "equitable lien" which arises in certain rare instances.

In the US and Canada the word is usually , whereas in the UK and other countries it is usually /ˈliːən/.

Despite their differences in terminology and application, there are a number of similarities between liens in the U.S. and elsewhere in the common law world.

United States

Liens can be consensual or non-consensual (also termed voluntary or involuntary in different states). Consensual liens are imposed by a contract between the creditor and the debtor. These liens include:

• mortgages;
• car loans;
• security interests;
• chattel mortgages;
• property improvements (mechanic's lien)

Non-consensual liens typically arise by statute or by the operation of the common law. These laws give a creditor the right to impose a lien on an item of real property or a chattel by the existence of the relationship of creditor and debtor. These liens include:

• tax liens, imposed to secure payment of a tax;
• "weed liens" and "demolition liens", assessed by the government to rectify a property from being a nuisance and public hazard;
• attorney's liens, against funds and documents to secure payment of fees;
• mechanic's liens, which secure payment for work done on property or land;
• judgment liens, imposed to secure payment of a judgment
• maritime liens, imposed on ships by admiralty law.

Liens are also "perfected" or "unperfected" (see perfection). Perfected liens are those liens for which a creditor has established a priority right in the encumbered property with respect to third party creditors. Perfection is generally accomplished by taking steps required by law to give third party creditors notice of the lien. The fact that an item of property is in the hands of the creditor usually constitutes perfection. Where the property remains in the hands of the debtor, some further step must be taken, like recording a notice of the security interest with the appropriate office.