When the automated player-piano was invented in the mid-19th century, companies that sold sheet music groused. When commercial radio took off, musicians bellyached that it would destroy them. So too, with the introduction of gramophones and tape recorders, did established businesses of the day try to block the inventions to protect their commercial interests. In each case, public interest defeated the private, and the technologies flourished (often, ironically, to the benefit of the party that originally objected). For instance, movie studios tried to outlaw Sony's Betamax because it could be used to infringe film copyright. In 1984, America's Supreme Court ruled the devices legal because they were 'capable of substantial non-infringing uses.' Today, the homevideo market is almost three times larger than Hollywood box-office receipts. On March 29th, the Supreme Court heard oral arguments regarding peer-to-peer (P2P) file-sharing software. This lets internet users obtain files of, say, music or video quickly and inexpensively by cleverly sharing the content among many users. In over 90% of the cases, the files downloaded infringe copyrights. Some 28 entertainment companies have joined together against two P2P software makers, StreamCast Networks and Grokster, claiming that they are accountable for 'secondary liability' of copyright infringement because they knowingly turn a blind eye to the illegal activities of users. The entertainment industry is arguing that business models predicated on the theft of intellectual property should be declared illegal. Technology firms counter that to restrict companies according to how their technology is used by customers would hand media firms a veto power over technical innovation any time it seems to threaten their interests. The Supreme Court will have to reexamine its 1984 Betamax decision in light of the internet and digital devices from the PC to the iPod and digital video recorders. One lower court has found that P2P software makers are not liable, because the product is capable of legal uses. But another court interpreted the 1984 ruling differently, finding against P2P by highlighting the ruling's indication that there should be 'commercially significant' non-infringing uses for 'legitimate' purposes. Recording companies complain that the decline in music sales in the past few years (save for a small uptick in 2004) is due large to illegal file-sharing. Millions of people use P2P systems, downloading 2.6 billion songs a month and 400,000 films a day, accounting for over half of all Internet traffic by some measures. Faced with the inability to get courts to shut down P2P networks, the industry has sued thousands of alleged pirates worldwide and backed legislation that would ban technologies that 'induce' infringement. A ruling against the P2P systems would slow, but would probably be too narrowly specific to end, the growth of firms exploiting the technology. A win for the media firms would help them negotiate agreements with the cottage industry of firms aiming to get into online music distribution. The entertainment industry would probably refocus its legal battles on targeting internet service providers. But the cost of this could be huge. It could dramatically set back the adoption of the many beneficial uses of P2P, from legitimate content distribution—such as individuals sharing their family photos or their home-recorded music online—to grid computing. Theft of intellectual property is wrong, of course. But technologies exist that can prevent it—and even let media firms harness the Internet to make money, as in the previous battles between content owners and new technologies. The Supreme Court should retain the Betamax principle. It is not the role of law to block innovation. What does the author mean by saying that 'public interest defeated the private, and the technologies flourished' (