Tonight's fight looks sure to smash all existing pay-per-view records - and after months of trash-talking, a world tour, and Friday night's weigh-in, fight night is finally here.
Saturday night will see out-of-retirement best boxer of his generation Floyd Mayweather facing the UFC's biggest star, Conor McGregor, in Sin City.
The T-Mobile arena in Las Vegas will be packed to the rafters but millions more will be watching the fight via TV around the world.
After a long period of speculation about whether the fight would ever take place, the last few months have featured high levels of animosity on both sides, as the rivalry heats up ahead of fight night.
This will either be a boxing bout for the ages or a cross-code money-spinning abomination, depending on your point of view.
Whichever camp you're in, here's all you need to know about the fight between the man with a 49-0 boxing record facing and the Irish fighter who has never taken part in a professional boxing fight.