UPDATE: Details are hazy. Microsoft now says there will be no fee to play used games.
The Xbox One won't play Xbox 360 games but it will play used games ... at a price.
With each new game that you buy, you'll have a unique code that links the game to your Xbox One console. That means every person that uses that console across multiple accounts will be able to play that game, irrespective of which user is signed in.
However, if you want to play the game on a friend's console, you'll need to pay a fee to unlock it and get it to work on the console, with the price relative to the game's age.
UPDATE: Microsoft has clarified, stating that as long as you're signed into one of the accounts connected to the game, you'll be able to use it on another console.
Microsoft corporate vice president Phil Harrison told Kotaku that a new game could be unlocked for the full price of the disc at stores.
"The bits that are on that disc, you can give it to your friend and they can install it on an Xbox One," he said. "They would then have to purchase the right to play that game through Xbox Live."
Harrison also revealed a game trading system through Xbox Live, although more details are being reserved for a later date.
"We will have a solution -- we’re not talking about it today -- for you to be able to trade your previously-played games online," Harrison said.