Supap Kirtsaeng bought textbooks published overseas by John Wiley & Sons and resold them on eBay and other websites for a profit in the United States. The publisher sued Kirtsaeng for violating its copyright, and the case went before the Supreme Court last week.

At stake in this important and knotty case is whether copyright holders -- publishers, filmmakers, musicians and creative artists of all sorts -- can sell their copyrighted works abroad at prices different from what they charge in the American market and rely on copyright law to help maintain the separate pricing without having importers profit from the difference. The justices should rule that the Copyright Act and a revision to it that Congress made in 1976 prohibit such resales.

A federal trial court ordered Kirtsaeng to pay $600,000 in damages for infringing on the Wiley copyright by reselling more than 600 copies of eight different books that he bought in Thailand. Kirtsaeng contends that the law allows him to resell the textbooks because he, family members and friends bought them legally and a principle called the first-sale doctrine, announced by the Supreme Court in a 1908 ruling and codified into law by Congress, says copyright owners cannot control the distribution and pricing of works, like books, after the initial sale.

But the Copyright Act prohibits anyone from importing into the United States copyrighted works without the copyright holder's approval. That provision would be seriously limited if copies of a work made abroad could be resold by importers in this country without constraint.

This case requires a difficult interpretation of the Copyright Act, but that is made easier by understanding the intent of Congress when it revised the law in 1976. It did so to broaden protection against unauthorized imports of copyrighted works by so-called gray-market sellers, and to make easier the kind of market segmentation by geography and price that Kirtsaeng's resales subverted.

With segmentation, book publishers can offer cheaper editions of their works in less-developed countries, without concern that those copies will be resold in the United States and unfairly undercut sales here.