The auction house overhaul is fairly major, with a new "stock market" buy/sell model allowing players to see all items of a particular type and price on a single line. Buyers will see the lowest five prices for an item, and can purchase items by providing the bid price they're willing to pay. The revamped auction house will then reconcile the transaction with the listing seller(s) on a first-come first-serve basis. The auction house UI has also been redone, and 1.37 also brings a new preview function for displaying items on your avatar prior to purchase.
Be sure and read up on all the incoming changes via the patch notes on the official website.