The Halo series, set in a future when humanity is battling a hostile alien race, has sold more than 14.8 million copies since its debut in 2001, making it one of the most successful game franchises. The last major game in the series, Halo 2, set a record in 2004 for first-day sales of any entertainment product, generating more than $125 million in the United States in its first 24 hours. Microsoft and major game retailers expect to surpass that mark beginning at midnight tomorrow, when more than 10,000 stores across the country will open to sell Halo 3. In London, authorities have banned official "midnight madness" events amid fears of unruly crowds.

As early as July more than 1 million consumers had ordered the game, which will be available in three versions, costing $60, $70 and $130. (The top version comes with a space helmet inspired by Halo 3.) The game will ship in 17 languages. "There is no question the Halo 3 launch is the biggest event of the year in video games, and for a lot of people it will be the biggest entertainment event of the year, period," said Andy McNamara, editor in chief of the magazine Game Informer. "Halo just has its tendrils into the imagination of a whole generation. Frankly, I don't know if Microsoft would even be in the game business today if it weren't for Halo."

Halo 3 is widely expected to be the top-selling game of the year for Microsoft's Xbox 360 console, the sole machine on which the game can be run. Halo 3 is also expected to drive users toward the company's Xbox Live Internet service. The only other release that had been expected to compete with Halo 3 this coming holiday season was Take-Two's Grand Theft Auto IV, often called G.T.A., but that game was recently delayed until next year. "Halo 3 is the drive title for Xbox 360 to bring it to the next level, and given the fact that G.T.A. slipped into next year, Halo 3 is really in a league of its own this year," said Ben Schachter, an Internet and video-game analyst at UBS Securities. "Certain games, like Halo, have a special place, and they can help drive the entire industry forward."

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"People have been talking about video games becoming a bona fide mainstream entertainment medium, and you really see that playing out with Halo," said Neal Tiles, president of G4, which will begin its coverage in New Zealand, where the game will first arrive. "They're looking at $150 million in the first day, which is bigger than any movie has done. Culturally, it's at least as big as any film opening or TV premiere or book or Broadway opening, and probably bigger."