Property tax, millage tax is an ad valorem tax that an owner of real estate or other property pays on the value of the property being taxed. There are three species or types of property: Land, Improvements to Land (immovable man made things), and Personalty (movable man made things). Real estate, real property or realty are all terms for the combination of land and improvements.

The taxing authority requires and/or performs an appraisal of the monetary value of the property, and tax is assessed in proportion to that value. Forms of property tax used vary between countries and jurisdictions.

There is a form of tax which is often confused with the property tax. This is the special assessment tax. These are two distinct forms of taxation: one (ad valorem tax) relying upon the fair market value of the property being taxed for justification, and the other, (special assessment) relying upon a special enhancement called a "benefit" for its justification.

The property tax rate is often given as a percentage (amount of tax per hundred currency units of property value). It may also be expressed as a permille (amount of tax per thousand currency units of property value), which is also known as a millage rate or mill levy. (A mill is also one-thousandth of a dollar.) To calculate the property tax, the authority will multiply the assessed value of the property by the mill rate and then divide by 1,000. For example, a property with an assessed value of US$ 50,000 located in a municipality with a mill rate of 20 mills would have a property tax bill of US$ 1,000.00 per year.