On paper, both apps offer similar functionality. But YouTube Music has the added bonus of being able to tap into the vast archive of YouTube for its music, as well as the videos that go alongside this.
At the UK launch of YouTube Music and YouTube Premium, TechRadar asked T Jay Fowler, head of product at YouTube, exactly that question and it's something that the company is working very hard to figure out.
It turns out there is a very good reason the apps are currently co-existing: it's all about making sure that all functionality that Google Play Music users currently enjoy is eventually ported over to YouTube Music - as it stands, this just isn't the case.
Bringing YouTube Music and Google Play Music together
"We are working very hard to bring the two experiences together," said Fowler to TechRadar. "Supporting two apps on the market does come with some challenges and there are some beloved features in Google Play Music that we are in the process of building [into YouTube Music].
"But until we have those features we have a commitment to those users."
When it comes to the specific features, Fowler pointed out user profiles, bringing over users' playlists and, most importantly, the locker service. This is the section of Google Play Music where users upload their current music collections to the cloud, ready to stream wherever they want.
"We are working as fast as we can to bring them together," notes Fowler.
YouTube Music and YouTube Premium have just launched in the UK and are out now in 17 countries in total, including Australia and the US.
If you are already a subscriber to Google Play Music, then you will automatically get access to YouTube Music.
- YouTube Music and YouTube Premium: how Google is taking on Spotify and Netflix
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Marc Chacksfield is the Editor In Chief, Shortlist.com at DC Thomson. He started out life as a movie writer for numerous (now defunct) magazines and soon found himself online - editing a gaggle of gadget sites, including TechRadar, Digital Camera World and Tom's Guide UK. At Shortlist you'll find him mostly writing about movies and tech, so no change there then.