World of Warcraft Classic was announced at Blizzcon 2017, but when does it come out?
During Blizzcon 2018, Blizzard announced that WoW Classic will be released in Summer 2019. Access to WoW Classic will be included in the standard World of Warcraft subscription.
An exact release date is still TBA.
Update 5/14/2019: Blizzard has announced via Twitter that WoW Classic will go live on August 27, 2019. In addition, there will be beta testing prior to release so players who are a part of the beta may be able to play even sooner.