ArticleA US court said that the recording industry's methods to find music swappers are not allowed by the law.
In a separate ruling, the Dutch Supreme Court decided that the popular file-sharing program, Kazaa, is not breaking the law
The rulings are a blow to the record industry, which is trying to stop the illegal sharing of music online.
The music industry says the widespread copying of music over the internet is partly to blame for a drop in CD sales worldwide.
It has turned to the courts to try to stop people downloading music for free over the internet.
One of the more controversial tactics was legal action against individuals accused of sharing music files online without permission.
The Recording Industry Association of America had issued hundreds of subpoenas to force internet providers, such as Verizon, to identify customers suspected of file-swapping.
But Verizon argued that existing copyright law did not give the recording industry the power to force it to hand over names and addresses of their subscribers.
A three-judge panel has now agreed with its interpretation of the law, overturning an earlier ruling that had approved the use of subpoenas.
The ruling by the US appeals court may force a change in tactics by the music labels.
There was more bad news for the record labels, this time from the Dutch Supreme Court.
This decision has no bearing at all on the single most important fact, which is that people who are distributing copyrighted music over such systems, and that means the vast bulk of all users, are breaking the law
Allan Dixon, IFPI
It ruled that the world's most popular file-sharing program, Kazaa, was not breaking the law.
The Dutch court said that the developers of the software could not be held responsible for how individuals used it.
"The victory by Kazaa creates an important precedent for the legality of peer-to-peer software, both in the European Union and elsewhere," said Kazaa's lawyers Bird & Bird, in a statement.
The founders of Kazaa, Niklas Zennstroem and Janus Friis, described the ruling as an "historic victory for the internet and consumers".
The reaction from the music industry was to criticise the ruling as "one-sided".
"The Dutch judgement is flawed because it was based on a one-sided presentation of the facts as put forward by Kazaa," said Allen Dixon, Director of the International Federation of the Phonographic Industry, a music trade body.
"In any case, this decision has no bearing at all on the single most important fact, which is that people who are distributing copyrighted music over such systems, and that means the vast bulk of all users, are breaking the law."
Kazaa has long since replaced Napster as the main file-sharing service, with more than 17 million registered users in Europe and the US.