Hurdling is running over obstacles. In track and field athletics there are sprint hurdle races and long hurdle races. The standard sprint hurdle race is 110 meters for men and 100 meters for women. The standard long hurdle race is 400 meters for both men and women. Each of these races is run over ten hurdles and they are all Olympic events.

Other distances are sometimes run, particularly indoors. The sprint hurdle race indoors is usually 60 meters for both men and women, although races 55 meters or 50 meters long are sometimes run. A 60 meter indoor race is run over 5 hurdles. A shorter race may have only 4 hurdles. The long hurdle race is sometimes shortened to 300 meters or 200 meters.

There are two basic hurdle heights: high hurdles and intermediate hurdles. The sprint hurdle races (60 m, 100 m and 110 m) use high hurdles, which are 42 inches (1.07 m) high for men and 33 inches (.84 m) high for women. Long hurdle races (400 m) use intermediate hurdles, which are 36 inches (.914 m) high for men and 30 inches (.762 m) high for women. Slightly lower heights (generally 3 inches lower) are sometimes used in youth or high school events, especially for boys.

In sprint hurdle races for men, regardless of the length of the race, the first hurdle is 15 yards (13.72 m) from the starting line and the distance between hurdles is 10 yards (9.14 m). In sprint hurdle races for women, the first hurdle is 13 m from the starting line and the distance between hurdles is 8.5 m. In long hurdle events, whether for men or women, the first hurdle is 45 meters from the starting line and the distance between hurdles is 35 m. Any race which is shorter than the standard distance is simply run over fewer hurdles; hurdle placement is the same as in the standard race.

A modern hurdle will fall over if a runner hits it. There is no penalty for hitting a hurdle (provided this is not judged deliberate), although it usually slows a hurdler down. However, pushing the hurdle with one's hands or running out of one's lane as a result of hitting the hurdle is cause for disqualification. While hitting hurdles is not generally considered desirable, there have been a few sprint hurdlers who have been successful despite knocking over a lot of hurdles.

Hurdling requires both great running speed and excellent technique. Good hurdlers "run through" hurdles rather than jumping over them. Hurdlers will generally go over the hurdles using the same lead leg each time, taking three strides between hurdles in the sprint events and 13, 15 or even 17 strides between hurdles in the long hurdle races (although 12 has been done competitively; see Edwin Moses). In a long hurdle race, a runner may take 13 strides between hurdles early in the race but be forced to increase the number of strides as fatigue sets in. Some hurdlers may go to an even number of strides, which requires them to switch lead leg.

The 400 meter intermediate hurdle race is one of the most demanding in athletics (it is sometimes called the "man-killer event"). It combines a very long sprint with the technical and physical demands of hurdling.

Another demanding event in which runners must negotiate obstacles is the steeplechase, which is not considered a hurdle race. Steeplechase barriers are the same height as intermediate hurdles but steeplechase barriers are solid and will not fall over if hit. Runners often step on barriers as they go over them. Another difference is that the steeplechase is a distance race rather than a sprint.

There are also shuttle hurdle relay races, although they are rarely run. In a shuttle hurdle relay, each of four hurdlers on a team runs the opposite direction from the preceding runner. The standard races correspond to the standard sprint hurdle races: 4 x 110 m for men and 4 x 100 m for women.