The Supreme Court case concerns something called the "first-sale doctrine" in copyright law. Simply put, the doctrine means that you can buy and sell the stuff you purchase. Even if someone has copyright over some piece of your stuff, you can sell it without permission from the copyright holder because the copyright holder can only control the "first-sale." The Supreme Court has recognized this doctrine since 1908.

To use a classic example, imagine you buy a novel by Sabina Murray. Sabina owns the copyright to the book, so you can't make a copy of the book. But you bought a copy of the book, and can sell the copy to anyone who'll pay you for it. You can sell it to a neighbor, to a fellow student, or to someone else on Craigslist or on eBay.

But the first-sale rule doesn't just make it possible to sell your books and other creative works like CDs, paintings, or DVDs. Almost every product made now has a copyright logo on it. That logo, alone, empowers manufacturers to sue people for copyright infringement for unlawful sales.

The first-sale doctrine is one thing that makes it lawful to sell almost any good. The companies that have gone to court and sued over selling their "copyrights" include a watchmaker and shampoo producer. They have gone to court arguing that one part of the Copyright Act -- which gives them a right against unauthorized imports -- invalidates the first-sale doctrine.

In 1998, the Supreme Court ruled that the first-sale doctrine applies to any product manufactured in the United States, sold in the U.S., even if the first sale by the copyright holder was abroad and the item was imported back into the U.S. This decision was unanimous and rejected the interpretation preferred by the U.S. government's lawyer -- and the biggest copyright holders.

The legal confusion today concerns only products made abroad.

Continuing a long string of similar cases, the Supreme Court will review a New York federal court decision that decided, in short, that the first-sale doctrine does not apply to any copyrighted product manufactured abroad. That case concerns textbooks.

John Wiley & Sons, a textbook publisher, sells expensive versions of the textbooks here and less expensive versions abroad. Supap Kirtsaeng, a foreign graduate student at University of Southern California, decided to help pay for his schooling by having relatives buy him copies of the foreign versions abroad, send them to him, whereupon he'd sell those books on eBay to willing students. He'd make money, the students would save money, but Wiley might have fewer sales of its pricey American versions. The case is styled Kirtsaeng v. John Wiley & Sons.

Both the District and Second Circuit courts held that any product manufactured abroad is not subject to the first-sale doctrine. For instance, that iPad you sold. You noticed this statement: "Designed by Apple in California. Assembled in China." Same for the iPods you've owned, the iPhones, and the MacBooks. Because those products were manufactured abroad, according to the Second Circuit, the first-sale doctrine doesn't apply to them. You need the permission of every copyright holder to sell the iPad.