The 400 metres hurdles is an Olympic athletics event in track and field. On a standard outdoor track 400 metres is the length of the inside lane once around the stadium. Runners stay in their lane the entire way after starting out of the blocks and must clear ten hurdles that are evenly spaced around the track. The hurdles are positioned so that they fall forward if bumped into to prevent injury to the runners. Although fallen hurdles don't count against them, runners like to clear them clean, as touching them during the race slows runners down.

The best male athletes can run the 400 m hurdles in a time of around 47 seconds, while the best female athletes achieve a time of around 53 seconds. The current men's and women's world record holders are Kevin Young with 46.78 seconds and Yuliya Pechonkina with 52.34 seconds. Compared to the 400 metres, the hurdles race takes the men about three seconds longer and the women four seconds longer.

The 400 m hurdles have been an Olympic discipline since 1900 and 1984 for men and women, respectively.

The 400 metres, or 400 metre dash, is a common sprinting event in track and field competitions. It has been featured in the athletics programme at the Summer Olympics since 1896 (1964 for women). On a standard outdoor running track, it is exactly one lap around the track. Runners start in staggered positions and race in separate lanes for the entire course. In many countries, athletes previously competed in the 440 yard dash (402.336 m)—also referred to as the 'quarter-mile'—instead of the 400 m, though this distance is now obsolete. An athlete who competes in the 400 m may still be referred to as 'quarter-miler'.

Maximum sprint speed capability is a significant contributing factor to success in the event, but athletes also require substantial speed-endurance and the ability to cope well with high amounts of lactic acid to sustain a fast speed over a whole lap. Whilst considered to be predominantly an anaerobic event, there is some aerobic involvement and the degree of aerobic training required for 400 metre athletes is open to debate.^{[citation needed]}