The Antikythera mechanism is one of the world's oldest known geared devices. It has puzzled and intrigued historians of science and technology since its discovery. Following decades of work cleaning the device, in 1951 British science historian Derek J. de Solla Price undertook systematic investigation of the mechanism. In June 1959, Price's "An Ancient Greek Computer" was the lead article in Scientific American. Price advanced the theory that the Antikythera mechanism was a device for calculating the motions of stars and planets, which would make the device the first known analog computer. Until that time, the Antikythera mechanism's function was largely unknown, though it had been correctly identified as an astronomical device, perhaps being an astrolabe.

In 1971 Price, by then the first Avalon professor of science history at Yale University, teamed up with Charalampos Karakalos, professor of nuclear physics at the Greek National Centre of Scientific Research "DEMOKRITOS". Karakalos had gamma- and X-ray analysis carried out on the mechanism, which revealed critical information about the device's interior configuration. In 1974 Price wrote "Gears from the Greeks: the Antikythera mechanism — a calendar computer from ca. 80 B.C.", where he presented a model of how the mechanism could have functioned. Recent research breakthroughs confirm Price's theory (see below).

The device uses a differential gear, previously believed to have been invented in the 16th century, and is remarkable for the level of miniaturization and complexity of its parts, which is comparable to that of 18th century clocks. It has a differential gear arrangement with over 30 gears, with teeth formed through equilateral triangles. When past or future dates were entered via a crank (now lost), the mechanism calculated the position of the Sun, Moon or other astronomical information such as the location of other planets. The use of differential gears enabled the mechanism to add or subtract angular velocities. The differential was used to compute the synodic lunar cycle by subtracting the effects of the sun's movement from those of the sidereal lunar movement. It is possible that the mechanism is based on heliocentric principles, rather than the then-dominant geocentric view espoused by Aristotle and others. This may indicate that the heliocentric view was more widely accepted at the time than was previously thought.

It is probable that the Antikythera mechanism was not unique. Cicero, writing in the 1st century BC, mentions an instrument "recently constructed by our friend Posidonius, which at each revolution reproduces the same motions of the sun, the moon and the five planets." (Cicero was himself a student of Posidonius.) Similar devices are mentioned in other ancient sources. It also adds support to the idea that there was an ancient Greek tradition of complex mechanical technology that was later transmitted to the Muslim world, where similar but simpler devices were built during the medieval period. The early 9th century Kitab al-Hiyal ("Book of Ingenious Devices"), commissioned by the Caliph of Baghdad, records over a hundred mechanical devices described in Greek texts that had been preserved in monasteries. Such knowledge could have yielded to or been integrated with European clockmaking and ancient cranes.

The device's full range of capabilities is unknown. Some investigators believe that the Antikythera mechanism could have been used to track celestial bodies for astrologically auspicious occasions such as religious events or births. Price suggested that it might have been on public display, possibly in a museum or public hall in Rhodes. The island was known for its displays of mechanical engineering, particularly automata, which apparently were a specialty of the Rhodians. To quote Pindar's seventh Olympic Ode:

The animated figures stand

Adorning every public street

And seem to breathe in stone, or

move their marble feet.