Halo 3, one of the most anticipated and heavily marketed video games in history, has gone on sale at thousands of stores across the US, Australia and New Zealand.
More than 10,000 US shops opened their doors to sell the title which is Microsoft's key weapon in the console wars with Sony and Nintendo.
More than 15m copies of the first two titles in the series have been sold.
Microsoft hopes day one sales of the game will top £70m ($140m).
If the game does bring in more than $140m, it will earn more in 24 hours than the opening box office takings of any movie in history.
However, sceptics point out that video games cost upwards of £40 ($80), while cinema tickets are much less.
In New York, about 500 people turned out for the midnight launch.
Gamer Alex Escobar, who was one of the first in the queue, told Reuters news agency: "It is worth it. It is time to finish this fight," echoing the tagline for the science fiction game.
Shane Kim, corporate vice president of Microsoft Game Studios, said the hoped for success of Halo 3 was an essential element in the competitive console market.
He said: "Halo 3 is the biggest franchise for Xbox. The game is going to drive a lot of Xbox 360 sales and Xbox Live subscriptions this Christmas."
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