I missed this bit of news earlier when I put up the other Rainbow Six: Siege news today regarding the changes from the alpha, but it seems as though a release date was revealed. That date is October 13.
Today, Ubisoft announced that Tom Clancy’s Rainbow Six Siege, the latest in the best-selling Tom Clancy’s Rainbow Six franchise, will be available worldwide on October 13th 2015 on PlayStation 4 computer entertainment system, Xbox One, the all-in-one games and entertainment system from Microsoft and Windows PC.

Developed by Ubisoft Montreal, Tom Clancy’s Rainbow Six Siege is inspired by real world counter-terrorist organizations, and puts players in the middle of lethal close-quarters confrontations. For the first time in a Tom Clancy’s Rainbow Six game, players will choose from a variety of unique Counter Terrorist Operators and engage in intense sieges, a new style of assault where enemies have the means to transform their environments into modern strongholds while Rainbow Six teams lead the assault to breach the enemy’s position.