Ubisoft is letting everyone register for the upcoming Rainbow Six Siege closed beta.
Rainbow Six Siege is due for a closed beta sometime this year. Ubisoft has opened registration to everyone. All you need to do is enter your preferred platform and log in using your Uplay account.
You will be entered into a waiting list, so access is not guaranteed. The only way to guarantee entry is to pre-order the game.
The game is currently in closed alpha with a limited number of users. The beta will surely be more polished than the alpha.