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If you do not have a Steam account, you will need to download the client from the official website, install it and then create your account. Once you are logged into your account, click on "Add game" in the bottom left corner and then on "Activate product on Steam". After a few clicks on "Next", you can finally enter your CD key, the game will automatically be added to your library and the download will begin.

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The Battle.net activation process is quite simple. First you need to create a Battle.net account by visiting the official website and clicking on "Create Account". Then log into your Battle.net account and click on "Add Game" to add the game you want to activate. Then enter the activation code that came with the game and follow the on-screen instructions to complete the activation process. Once activation is complete, you can download and install the game on your computer.

Battle.net Diablo III Global Play FAQ : Learn more about the new feature allowing to play Diablo III on Americas/Asia/Europe Regions from any Game key versions.

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