Looks like they decided to get the ball rolling a bit early, though. The game just went live on the iOS and Android app stores in the US and UK, one day earlier than advertised. Wands at the ready!
As expected (and as with Pokémon GO) the launch is being rolled out on a country-by-country basis, rather than going live for the entire world all at once. It’s spent the last few weeks in a kinda-sorta-Beta phase, available in Australia and New Zealand to those who didn’t mind dealing with some pre-launch bugs. Today it rolled out to the US/UK, and it’ll open up to more countries as Niantic determines its servers are up for it.