As sites were created for aggregating news, photos, and videos, the obvious next step was music. Music sites, such as Last.fm and Pandora, provide users with recommendations. These suggestions are based on the preferences of others who have similar musical interests as you. Therefore, the site bases its recommendation system on user input. If someone votes yes to two songs, the site then forms associations between liking one song and the other.
The obvious complication has been copyright infringement, which has threatened to shut these types of sites down. However, the sites do not allow users to download music and they have largely managed to stay up and running. Essentially, the reason for this is because they function as radio stations—and pay broadcast fees as radio stations. When you listen to a service such as Last.fm, you have some control over what types of songs are played, but you don’t have complete control and you don’t get the rights to the song. This a compromise worked out to let users explore new music for free, yet not infringe on the rights of artists and their record labels.