In the classic Monopoly board game, an unowned property a player declines must be auctioned by the bank.
When a player lands on an unowned property, they may buy it for the printed price. If they decline, the banker conducts an auction, and any player may bid, including the player who originally declined. The property goes to the highest bidder, who pays the bank the winning amount.
This rule is frequently omitted in casual games, where an unwanted property may simply remain unowned. That house rule can make the game longer and reduce the amount of property entering circulation. Under the official rules, an auction can also produce a price below the printed purchase price if bidding is low.
The banker manages the auction but does not own the property. The rule applies to purchasable spaces such as streets, railroads, and utilities, not to tax spaces or the board’s special corners.