The men's 400 metres at the 2008 Summer Olympics took place on 18–21 August at the Beijing National Stadium.

Jeremy Wariner took silver to become the fourth man to win two medals in the event, though Merritt kept him from matching Michael Johnson's pair of golds.

The defending champion was Jeremy Wariner, who also won World Championship titles in 2005 and 2007 preceding the 2008 Olympics.

[4] Wariner started fast in the final: running in lane 7, he caught up with Martyn Rooney to his outside making up the stagger before the 200 mark.

Further outside but more difficult to calculate, David Neville was also out fast, while Merritt was even relative to the stagger against Chris Brown in lanes 4 and 5.

Once they hit the straightaway, it was Merritt who had the speed, sprinting away with a high knee action that increased his gap over Wariner and Neville.

Merritt sped away to a personal best 43.75, Wariner gave up the chase and jogged across the finish line in second, barely ahead of Brown, who looked like he had passed Neville.

But it is the torso that counts and Neville's body crossed the line in third, .04 ahead of Brown and .06 behind Wariner.

The top two runners in each semifinal heat and the next two fastest overall advanced, making an eight-man final.