This list of 360 games playable on Xbox One records all backward-compatible 360 and XBLA games confirmed to function on current-gen hardware. At the moment, these games are only playable by members of the Xbox Preview Program.
Updated: Gears of War is working today! Three new games will be backward compatible this fall, indicated by an asterisk below. Additionally, Microsoft's Major Nelson tweeted that Shadow Complex will be backward compatible.
Microsoft announced Xbox One backward compatibility at E3 2015 and is rolling out the function starting this year. 360 discs do not play natively but trigger a download of a compatible file, while downloadable titles appear automatically.
Games currently compatible include:
A Kingdom for Keflings
A World of Keflings
Alien Hominid HD
Gears of War
Gears of War 2*
Gears of War 3*
Gears of War: Judgement*
Geometry Wars Evolved
Perfect Dark Zero
Shadow Complex (Date/time available TBD)
Super Meat Boy
Toy Soldiers: Cold War
Viva Piņata: TIP
Microsoft has also added a specific section titled "Backwards Compatibility" on their Xbox Feedback page for the purpose of allowing users to vote on which games they may want added to the list of backwards compatible games, although this list is not a guarantee that the games will be added in the future.