Sword swallowing is a skill in which the performer passes a sword through the mouth and down the esophagus to the stomach. This feat is not swallowing in the traditional sense. The natural processes that constitute swallowing do not take place, but are repressed to keep the passage from the mouth to the stomach open for the sword. The practice is dangerous and there is risk of serious injury or death.

Sword swallowing spread to Greece and Rome in the 1st century AD and to China in the 8th century. In Japan, it became a part of the Japanese acrobatic theatre, Sangaku, which included fire eating, tightrope walking, juggling and early illusion. In Europe, it developed into yet a third distinct type of performance associated with the medieval jongleurs, that of the street performance.

Sword swallowing was performed during the Middle Ages as part of street theatre and was popular at festivals and other large gatherings. It began to die out in the mid-19th century and was outlawed in Scandinavia in 1893. Prolific swallower Teodor Olsen famously made an appeal to Haakon VII of Norway, who was not swayed by his performance enough to rescind the ban.

According to an early-19th-century English magazine article the abilities of sword-swallowers in India were considered incredible when first reported in England. In 1813 'swallowing the sword' was advertised as among the new and astonishing feats performed by the Indian Jugglers then appearing in London. The troupe was led by the famous juggler and sword swallower Ramo Samee, who continued to perform until his death in London in August 1850, having at times also toured Europe and America. From 1850 to the 1890s a small number of sword swallowers performed in the UK, such as Martha Mitchell (c. 1855) and Benedetti (1863–1895), and in the US, including Lawson Peck (c. 1850s), Ling Look (c. 1872), Wandana (d. 1875), and Harry Parsons (d. 1880). The best-known North American sword swallower of this time was Fred McLone, better known to the public as "Chevalier Cliquot", who performed from 1878 to the early 20th century.

In 1893, sword swallowing was featured at the World Columbian Exposition at the Chicago World's Fair.

In the early 1900s, traveling circuses and sideshows featured sword swallowers. In Europe performers tried to swallow large numbers of swords; in America there was a focus on the novel and bizarre.^{[clarification needed]} Some tried to swallow longer swords, many swords, hot swords, bayonets or glowing neon tubes. Sword swallowers appeared on the same bill as magicians, such as Houdini. Western Europe and England also saw an increase in sword swallowing interest during this period, with many cross-Atlantic influences. During the late 19th century and early 20th century, traveling magic shows from the Orient toured Europe and America; some included sword swallowing. The middle of the 20th century saw a demise in circuses in general and sideshows in particular.

The performer must first lean the head back, hyper-extending the neck, and relax the upper esophageal sphincter (a generally involuntary muscle that contracts the top of the esophagus). Retching must be controlled while the sword, lubricated by saliva, is inserted through the mouth and past the pharynx.

According to a study on eight "normal subjects", the transverse diameter of the pharynx at its smallest point is on average 1.7 ± 0.5 cm (0.67 ± 0.20 in).