The 10-second barrier is the physical and psychological barrier of completing the 100 metres sprint in under ten seconds. The achievement is traditionally regarded as the hallmark of a world-class male sprinter. Its significance has become less important since the late 1990s, as an increasing number of runners have surpassed the ten seconds mark. The current men's world record holder is Usain Bolt, who ran a 9.58 seconds at the 2009 IAAF World Championship final.

Jim Hines was the first person to ever officially run the 100 metres under 10 seconds at the 1968 Mexico City Olympics. The fastest non-winning sub-10 performance was by Tyson Gay who clocked 9.71 in 2009 as a runner-up. The only quadragenarian to have run a sub-10 is Kim Collins who ran his personal best time of 9.93 in 2016 at 40 years old, earning him the nickname Ageless Wonder. Justin Gatlin chronologically held the longest streak of sub-10 performances in history, having a sub-10 career in a time-span of 18 years, from his first sub-10 clocking in 2003, to the final one in 2021. In 2025, Akani Simbine became the first athlete in history to run under 10 seconds in the 100 m for 11 seasons in a row. That surpassed the previous record of 10, held by Bolt. The most competitive 100 m sprint races completed in sub 10 seconds is 97 races and was achieved by Asafa Powell between 12 June 2004 and 1 September 2016.

For sprints, World Athletics (formerly known as IAAF) maintains that world records and other recognised performances require: a wind assistance of not more than two metres per second (2.0 metres per second (4.5 miles per hour)) in the direction of travel; fully automatic timing (FAT) to one hundredth of a second; and no use of performance-enhancing substances.^[4] Wind gauge malfunctions or infractions may invalidate a sprinter's time.^[6]

Prior to 1977, FAT was not required for IAAF official timings. Times were recorded manually to one tenth of a second; three official timers with stopwatches noted when the starting gun flashed and when the runner crossed the finish line, and their median recorded time was the official mark. Some races also had an unofficial FAT, or semi-automatic time, often in conjunction with photo finish equipment. The first person timed at under ten seconds was Bob Hayes, who ran 9.9 seconds at the Mt. SAC Relays in April 1963, but with a tailwind of 5.0 m/s (11.2 mph). Hayes clocked another illegal 9.9 (wind 5.3 m/s (11.9 mph)) in the semi-final of the 1964 Olympic 100 metres, with the first sub-10 FAT of 9.91 seconds. In the final, Hayes' official tenths time of 10.0 seconds was calculated by rounding down the FAT of 10.06 seconds; the backup hand-timers recorded 9.8, 9.9, and 9.9, which would have given 9.9 as the official time if the FAT had malfunctioned. At the 1968 USA Outdoor Track and Field Championships at Charles C. Hughes Stadium in Sacramento, California, three men ran legal hand-timed 9.9 seconds: Jim Hines first and Ronnie Ray Smith second in the first semi-final, and Charlie Greene first in the second semi-final. This was dubbed the "Night of Speed", and all three were recognised as world records by the IAAF. The IAAF lists their FATs as: Hines 10.03, Smith 10.14 and Greene 10.10; although Time magazine reported at the time that "an automatic Bulova Accutron Phototimer confirmed that all three had indeed broken [10.0]". Hines also had a wind-assisted 9.8 seconds in the heats. Hines went on to win the 1968 Olympic final in 9.9 seconds, rounded down from his FAT of 9.95, making it the first non-wind-assisted electronic sub-10-second performance. By 1976, six other men had equalled the 9.9 hand-timed record, though none of their performances had an FAT mark.

After the 1977 rule change, Jim Hines' nine-year-old 9.95 was the only recognised sub-10-second race. That year the barrier was broken again, when Silvio Leonard ran 9.98 seconds on 11 August 1977. Both of these marks were recorded at a high altitude, which aids performance due to lower air resistance.

Carl Lewis was the first sprinter to break ten seconds at low altitude under electronic timing, with 9.97 seconds at the Modesto Relays on 14 May 1983. Calvin Smith recorded a world record of 9.93 seconds in Colorado Springs, Colorado on 3 July 1983, at altitude, and became the first sprinter to run under ten seconds twice, in August that year. In total, six sprinters legally broke the barrier during the 1980s. Another, Ben Johnson, had eclipsed both the 9.90 mark in 1987 and the 9.80 mark in 1988, respectively with 9.83 seconds and 9.79 seconds; however, both of these records were rescinded after he tested positive for, and later admitted to, using doping, namely steroids.

The 100 metres final at the 1991 World Championships represented a new zenith in the event: six athletes ran under ten seconds in the same race, and winner Carl Lewis lowered the world record to 9.86 seconds. In second place was Leroy Burrell who also broke the former world record, which had been his at 9.90 seconds. In third place, 0.01 seconds slower than the former world record, was Dennis Mitchell with a time of 9.91 seconds. In fourth place, breaking his own European record of 9.97 seconds, was Linford Christie with a time of 9.92 seconds.

Maurice Greene, in 1999, was the first athlete to run under 9.80. Usain Bolt surpassed 9.70 in 2008, and 9.60 in 2009.