My genius mixes are a little samey - there's 8 "rock" mixes, then one each of alternative, electronic, dance and indie. I figured it was using the (very inconsistent) local genre tags - songs mostly set to "rock" if anything, or labeled with crap like "electro indie hop" and "smoker's delight". A little rummaging around later and while I've not delved into the massive body of "rock" to see if it's all actually rock, there's now at least as much stuff labeled "alternative", and way more electronic than there was. Re-submitted to iTunes... but the configuration of the genius mixes remains unchanged. Maybe I need to dive into the ~25% of my library that's set to rock and thin it out before I'll see any change, but maybe it's not using local tags? If not, what does it use? A song fingerprint? Does the iTunes store keep data like Pandora does about a song's use of rhythmic syncopation and extensive vamping? Either way, I've caught the OCD genre organising bug now, so if anyone knows a tool that'll tag my music collection with something sensible then that'd be good. I tried musicbrainz's Picard app , but it doesn't seem to populate genre.