It has been reported that for those in Australia and Japan, you can download the Pokémon GO app on iOS and Google Play Stores (for free) right now. UPDATE: USA as well officially now. Check out our guide for the basics and tips on starting out!

Other countries may soon follow – we’ll update as news comes in.

Update: It is now out in the USA reportedly on the Play Store (Android-accessible), but it may take time to appear for all devices. You may encounter some issues as well – for instance, a message stating ‘Our servers are experiencing issues. Please come back later.’ has been encountered.

Updated – It is now out on Google Play Store and the iTunes store for USA. Canadians may have to wait some more however, along with European players.

iTunes (iOS)
Google Play (Android) 

Serebii.net confirms that micro-transactions exist if you wish to buy in-game currency with real money.

Thanks to Achromatic for the tip, and Zach for the confirmation about the American release.
Thanks to Luigi-San for the tip about the extra-official release in the US, and Team Fail for the clarification.
Cover image by Pebbles.