The Auction House is a formal trading system that's new to the franchise. It's similar to the system used on other online RPGs, like World of WarCraft, and allows players within a region to buy and sell items easily, and safely, between eachother. Almost everything you find in the game can be traded in this way, although it is not the only way to trade (just as in Diablo II, you can trade items with other players within the game).

It's an economy built entirely by the players - Blizzard will not be selling any items. And both in-game gold and real money can be used to purchase items from other players - Blizzard are keen to stress that using real money is entirely optional.

The auction house uses a single interface for all characters on your account. You can sell and buy items easily for any of the characters on your account thanks to the universal auction house account and a shared stash for your characters. You'll also be able to search for the best gear for multiple characters on the same account without having to log out.

When you create an auction the item is immediately removed from your inventory and placed on sale. Auctions of items such as equipment can be cancelled within 5 minutes, and auctions of commodities can be cancelled at any time. All of the auctions last 48 hours, and you can have up to 10 active auctions per auction house.

There are fees for using the auction house, as detailed below. Fees will only be charged if your item successfully sells, and will automatically be deducted from the item’s final selling price.

Equipment (weapons, armor, accessories, and other unique items):

Transaction Fee (Gold Auction House) - 15% of final sale price.
Transaction Fee (Real-Money Auction House) - $1.00 USD per item.
Transfer Fee (when sending proceeds to PayPal or other authorized payment-service providers) - 15% of amount being transferred.

Commodities (gems, materials, dyes, pages, recipes, and other non-unique items):

Transaction Fee (Gold Auction House) - 15% of final sale price
Transaction Fee (Real-Money Auction House) - 15% of final sale price
Transfer Fee (when sending proceeds to PayPal or other authorized payment-service providers) - 15% of amount being transferred.