[header] How to buy a tax lien certificate [title] Understand tax liens. [step] A tax lien represents an unpaid tax debt on a property. If a property owner does not pay their taxes within a certain time period (it varies by jurisdiction), tax collectors will put the unpaid taxes up for auction. 
It is through this auction process that you have the opportunity to purchase a tax lien. [substeps] In the auction the highest bidder wins.