The closed StarCraft 2: Legacy of the Void beta (for PC and Mac) has begun and invites to it are being sent out today.
That doesn't mean piles of keys being given away - it means certain Battle.net accounts will be selected for participation. There are a variety of things factored into this: system specs, SC2 activity and a bit of luck. You don't need to be an owner of previous SC2 games.
To opt in, go to your Bnet Beta Profile Settings and check the box for StarCraft. If you're a lucky one, you should see a welcome email in your Bnet email address inbox.
If you bought a (real or virtual) ticket to BlizzCon 2014 or the SC WCS 2014 Global Finals then your name should be on the list.
For now, the beta is multiplayer only. The Archon mode - two players managing one base - is in.
There are no NDAs on any coverage so expect a flood of it soon.