More than 50 million songs have been bought from Apple's iTunes music store, the company has said.
The Apple online store is only available in the US
The tracks sold exclude some 100 million songs being given away as part of a promotion with Pepsi.
It launched its online music store for Mac users in April 2003 and expanded it to Windows users in October.
Apple is the leading player in online music but it faces increasing competition from others seeking a slice of the market for digital downloads.
Apple said the 50 millionth tune was The Path of Thorns by Sarah McLachlan, purchased last Thursday.
"Crossing 50 million songs is a major milestone for iTunes and the emerging digital music era," said Apple boss Steve Jobs.
At the launch of the Windows version of the store last October, he set the target of 100 million songs by April this year, including those given away in the Pepsi promotion.
Apple has become the leading legitimate music download service.
Its online store offers more than 500,000 tracks at 99 cents (55 pence) a song.
Coca Cola has claimed success in Europe for its service
At the moment, the iTunes store is only available in the US. International versions of the online store are expected to be launched later this year.
"With over 50 million songs already downloaded and an additional 2.5 million songs being downloaded every week, it's increasingly difficult to imagine others ever catching up with iTunes," said Mr Jobs.
But existing services such as Napster and MusicMatch are racing to catch up.
And newcomers such as Coca-Cola's site, Mycokemusic.com, have enjoyed some success.
Last week it claimed it was Europe's biggest legitimate music site, with 10,000 songs sold every week.