“We designed Xbox One so game publishers can enable you to trade in your games at participating retailers. Microsoft does not charge a platform fee to retailers, publishers, or consumers for enabling transfer of these games.”
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You can only give them to people who have been on your friends list for at least 30 days and each game can only be given once.
Microsoft says "your friends and family, your guests and acquaintances get unlimited access to all of your games. Anyone can play your games on your console--regardless of whether you are logged in or their relationship to you." The company added that “Xbox One is designed so game publishers can enable you to give your disc-based games to your friends. There are no fees charged as part of these transfers. There are two requirements: you can only give them to people who have been on your friends list for at least 30 days and each game can only be given once.”
It's worth noting that Microsoft allows you to gift games to friends but they can't borrow them. Microsoft added that "loaning or renting games won’t be available at launch, but we are exploring the possibilities with our partners."
However, anyone can play games using your console. "Your friends and family, your guests and acquaintances get unlimited access to all of your games," Microsoft says. "Anyone can play your games on your console--regardless of whether you are logged in or their relationship to you."
Xbox One will also allow you to give up to 10 family members access to "log in and play from your shared games library on any Xbox One." Similar to Xbox 360, "a family member can play your copy of Forza Motorsport at a friend’s house. Only now, they will see not just Forza, but all of your shared games. You can always play your games, and any one of your family members can be playing from your shared library at a given time."