In the iTunes store, the hit song "Someone Like You" by Adele sells for $1.29. Head over to ReDigi, an online marketplace where people can resell the music files they've purchased, and there's the track for only 59 cents.

It's the very same soulful tune. The difference is that ReDigi calls the copy on its site "used" or "recycled" (it was originally sold on iTunes). These are terms usually applied to physical goods like worn novels or unwanted CDs, not the growing volume of songs, books, and games composed of easily shared, everlasting bits. ReDigi's plans—and the legal debate they have generated—touch on the changing nature of ownership in an increasingly digital age (see "A Cloud over Ownership").

The Massachusetts-based startup is applying a concept of ownership ingrained in U.S. law: that a person who buys creative work can resell the originally purchased copy. "You buy it, and you own it. You should be able to sell it," says ReDigi chief technology officer Larry Rudolph, who is also a computer science researcher on leave from MIT. "If you steal it, you shouldn't be able to sell it. It's very simple."