The Great Comet of 1744, whose official designation is C/1743 X1, and which is also known as Comet de Chéseaux or Comet Klinkenberg–Chéseaux, was a spectacular comet that was observed during 1743 and 1744. It was discovered independently in late November 1743 by Jan de Munck, in the second week of December by Dirk Klinkenberg, and, four days later, by Jean-Philippe de Chéseaux. It became visible with the naked eye for several months in 1744 and displayed dramatic and unusual effects in the sky. Its absolute magnitude – or intrinsic brightness – of 0.5 was the sixth highest in recorded history. Its apparent magnitude may have reached as high as −7, leading it to be classified as a Great Comet. This comet is noted especially for developing a 'fan' of six tails after reaching its perihelion.

Although the orbit of the comet is usually assumed to be parabolic (i.e. to be effectively unbound), recent work has provided evidence that the comet has an orbital period of about 350 to 400 years. That work suggests that it is the same as the Great Comet of 1402, as well as comets observed in 1032, 676 and 336 AD. If that is correct, the comet could next reach perihelion in 2097, when it could put on a show.

The comet was discovered on November 29, 1743, by Jan de Munck at Middelburg, and was independently sighted on December 9, 1743 by Klinkenberg at Haarlem, and by Chéseaux from the observatory at Lausanne on December 13. Chéseaux said it lacked a tail and resembled a nebulous star of the third magnitude; he measured the coma as five minutes across.

The comet brightened steadily as it approached perihelion. By February 18, 1744, it reportedly was as bright as the planet Venus (with an apparent magnitude of −4.6) and at this time displayed a double tail.

The comet reached perihelion about March 1, 1744, when it was 0.2 astronomical units from the Sun. At about this time it was bright enough to be observed in daylight with the naked eye. As it moved away from perihelion, a spectacular tail developed — extending well above the horizon while the comet's head remained invisible due to the morning twilight. In early March 1744, Chéseaux and several other observers reported an extremely unusual phenomenon — a 'fan' of six separate tails rose above the horizon.

The tail structure was a puzzle to astronomers for many years. Although other comets had displayed multiple tails on occasion, the 1744 comet was unique in having six. It has been suggested that the 'fan' of tails was generated by as many as three active sources on the cometary nucleus, exposed in turn to solar radiation as the nucleus rotated. As each area is exposed to sunlight it becomes active and ejects material. The rotation period calculated by this method is 4.8±0.4 hours.

It also has been proposed that the tail phenomenon was a very prominent example of the "dust striae" seen in the tails of some comets, such as Comet West and C/2006 P1 (McNaught).

Chéseaux, on March 9, was the last known observer in the Northern Hemisphere to see the comet, but it remained visible for observers in the Southern Hemisphere, some of whom reported a tail length of approximately 90 degrees on March 18. The comet was not seen after 22 April 1744.