Ubisoft has announced Rainbow Six Siege has been delayed to December 1.

The upcoming title was originally due to release worldwide on October 13, with today's delay pinned on adjustment and improvements across all game modes.

"We’ve decided to push the release date of Rainbow Six Siege to December 1, 2015 for all regions," explains a post. "This wasn’t an easy decision, but based on the feedback we’ve received, and based on our own internal tests, we felt there are adjustments and improvements we can make, including improving the co-op experience across all game modes, weapon and gadget balancing, as well as menu and interface navigation. We’re taking a little more time to make these changes, and we think it’s the right call.

http://uk.ign.com/articles/2015/08/18/rainbow-six-siege-delayed-to-december?

Well good luck to them, they may need it.

Gonna go up against Just Cause 3 huh. Interesting

My god, the first week of december will be insane.Just Cause 3, Tomb raider, Xenoblade Chronicles X and now Rainbow Siege.Oh boy oh boy

Releasing after all the other shooters Halo,Cod and Battlefront and whilst people will be fresh on Fallout 4 and RoTR singleplayer campaigns and on same day as Just Cause 3 that could be suicide.

The number of comments here just shows the interest in the game.
Bad for them, they are missing out on a lot of sales, and instead of being the first shooter on the market, they will now be the last.