One of the few checks on the rights of copyright holders to control the disposition of their intellectual property. The first sale doctrine allows an individual who knowingly purchases a copyright work the right to later sell that copy of the work regardless of the wishes of the copyright holder. It is this protection that allows for the existence of both the used book and the video rental industries in the United States.

The idea underlying the first sale doctrine is that after purchasing a book the purchaser actually owns that copy of the book and can do with it whatever the hell he wants to. While this may seem obvious, it is exactly opposite from the practice in most of the Western world. In nations that are members of the European Union intellectual property creators retain moral rights to their works and can control the disposition of them even after first sale.

First sale also doesn't typically apply to software, because software is usually licensed rather than sold. Since a license to use is all that's granted no sale has taken place, thus first sale does not come into play. Nor does it apply to newer dvd (and perhaps other media, but I've not seen any) titles which are also explicitly licensed rather than being sold. I've not been able to uncover any references that indicate one way or the other whether print media can be distributed while only granting a license, but it would fit the logic of the entire licensing position.