A property tax lien is a lien or claim for money due to a federal, state, or local government for unpaid and delinquent taxes. For example, the federal government may place a lien on a homeowner’s home or other real property for unpaid federal income taxes, and state and local governments (often counties) may place a lien on real property for unpaid income or property taxes.

The federal, state, or local government entity—also known as a taxing authority—may seek to recover payment for unpaid taxes by forcing the sale of the property on which the lien is placed in the foreclosure process—a process in which the validity of the lien and satisfaction (payment) for the lien is litigated or determined in court.

In Colorado, a property tax lien represents a legal claim against a property for unpaid property taxes. When property taxes are delinquent, the county in which the property is located may place a lien on the property. This lien ensures that the tax authority gets first claim over other creditors in regards to the property's value. If the taxes remain unpaid, the county can initiate a foreclosure process to enforce the lien, which may result in the property being sold at a public auction. The process for the sale of tax liens and the foreclosure of properties is governed by Colorado state statutes, specifically Title 39, Article 11, and Article 12 for tax liens and tax sales. The foreclosure process involves court proceedings to confirm the validity of the lien and to determine the final satisfaction of the debt owed. Federal tax liens for unpaid income taxes can also be placed on a homeowner's property, and these are governed by federal law, which also has its own procedures for enforcement.