A tax lien is a lien imposed by law upon a property to secure the payment of taxes. A tax lien may be imposed for delinquent taxes owed on real property or personal property, or as a result of failure to pay income taxes or other taxes.

In the United States, a federal tax lien may arise in connection with any kind of federal tax, including but not limited to income tax, gift tax, or estate tax.

Internal Revenue Code section 6321 provides:

Internal Revenue Code section 6322 provides:

The term "assessment" refers to the statutory assessment made by the Internal Revenue Service (IRS) under 26 U.S.C. § 6201 (that is, the formal recording of the tax in the official books and records at the office of the Secretary of the U.S. Department of the Treasury). Generally, the "person liable to pay any tax" described in section 6321 must pay the tax within ten days of the written notice and demand. If the taxpayer fails to pay the tax within the ten day period, the tax lien arises automatically (i.e., by operation of law), and is effective retroactively to (i.e., arises at) the date of the assessment, even though the ten day period necessarily expires after the assessment date.

In law, a lien (UK /ˈliːən/ or US /ˈliːn/) 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 USA, 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 USA, 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.