Microsoft has made Halo Wars available through the Games on Demand bit of Xbox Live Marketplace.
You can grab it for £19.99 either via your Xbox 360 or through the web interface.
Alternatively you could pick it up for 20 quid in shops, where it joined the Xbox 360 Classics collection last week.
Check out our Halo Wars review to see whether you fancy it.
Also on Games on Demand this week is Street Fighter IV, but for some reason its been limited to the US and Asia. We've contacted Capcom to ask why.