Publishers are the biggest obstacle facing some Xbox 360 games being backwards compatible on Xbox One, according to Microsoft.
Partner director of platform management Mike Ybarra explained that game selection is based on two factors. One is fan feedback - which it is assessing through an online poll now - and the other is whether publishers will allow their games to carry forward.
"The biggest challenge we have is getting the publishers and developers to approve them. Once we get the approval, it's pretty simple," he told Digital Spy at E3 2015.
"Then we look at, what's the fan feedback on titles that they want, what's the most used Xbox 360 games right now - we take all of that and prioritise the list based on that criteria."
When asked about Xbox Original games, Ybarra said that Xbox 360 games are "our focus".
"Right now we're really focused on the fan feedback that we have on getting 360 games there," he said. "We'll have to go look at the data and see what all the fan feedback is on Originals."