A "Command and Conquer: Red Alert 2" registration code is the serial number that comes with each copy of the game. It is usually located at the registration instructions or at the back of the jewel case.
According to Electronic Arts, the registration code is required to play the game and unlocks online features, such as game patches and updates. "Command and Conquer: Red Alert 2" is a real-time strategy video game developed by Westwood Studios; it was later acquired and published by Electronic Arts. The original version of the series was released in 1995 and quickly caught the interest of avid strategy war gamers.