Any official claim or charge against property or funds for payment of a debt or an amount owed for services rendered. A lien is usually a formal document signed by the party to whom money is owed and sometimes by the debtor who agrees to the amount due. A lien carries with it the right to sell property, if necessary, to obtain the money. A mortgage or a deed of trust is a form of lien, and any lien against real property must be recorded with the County Recorder to be enforceable, including an abstract of judgment which turns a judgment into a lien against the judgment debtor's property.

There are numerous types of liens including: a mechanic's lien against the real property upon which a workman, contractor or supplier has provided work or materials, an attorney's lien for fees to be paid from funds recovered by his/her efforts, a medical lien for medical bills to be paid from funds recovered for an injury, a landlord's lien against a tenant's property for unpaid rent or damages, a tax lien to enforce the government's claim of unpaid taxes, or the security agreement (UCC-1) authorized by the Uniform Commercial Code. Most liens are enforceable in the order in which they were recorded or filed (in the case of security agreements), except tax liens, which have priority over the private citizen's claim.