Derek Thompson covers the growth of music streaming:

This is at least the third destructive wave for the music industry in the last decade and a half. First, Napster and illegal downloading sites ripped apart the album and distributed song files in a black market that music labels couldn’t touch. Second, Apple used the fear and desperation of the record labels to push a $0.99-per-song model on iTunes, which effectively destroyed the bundling power of the album in the eyes of millions of music fans (even though country album sales are still pretty strong). For a decade, music sales plummeted. Third, digital radio and streaming sites got so good that now many music fans wonder why they need to buy albums in the first place. So, they don’t.