Last.fm has more than 15m active users, mostly concentrated in the UK, US, Germany, Poland, Brazil and Japan; the website recommends music and allows people to find other users with similar musical tastes.
It was founded five years ago by Martin Stiksel, Felix Miller and Richard Jones, who will stay on and run it independently from CBS in London.
CBS, which owns a large portfolio of radio stations in the US, said Last.fm's demographics "play perfectly to CBS's goal to attract younger viewers and listeners across our business".
Last.fm's management wrote in a blog post today that they had been approached numerous times before selling to CBS and had spent much time this year discussing future plans for Last.fm. In the post, Jones said that Last.fm was approached by CBS while contemplating raising some additional venture capital.
Jones wrote: "As you can imagine, we have been approached numerous times in the past few years from all the usual suspects regarding acquisitions and so on; CBS are one of the few companies who needed no explanation of what we are doing, and we were impressed at how progressive their plans are.
"This deal with CBS gives us a chance to really make Last.fm shine, and gives us more flexibility than other funding options would for doing all the crazy stuff we’re had scribbled on whiteboards for years.
"There is quite a sense of achievement at Last.fm HQ today, we see this is as a huge boost for Last.fm and we are confident that together with CBS we have the wherewithall to change the music industry, and way people interact with music for good."