The Pascaline (also known as the arithmetic machine or Pascal's calculator) is a mechanical calculator invented by Blaise Pascal in 1642. Pascal was led to develop a calculator by the laborious arithmetical calculations required by his father's work as the supervisor of taxes in Rouen, France. He designed the machine to add and subtract two numbers and to perform multiplication and division through repeated addition or subtraction.

There were three versions of his calculator: one for accounting, one for surveying, and one for science.

The accounting version represented the livre which was the currency in France at the time. The next dial to the right represented sols where 20 sols make 1 livre. The next, and right-most dial, represented deniers where 12 deniers make 1 sol.

Pascal's calculator was especially successful in the design of its carry mechanism, which carries 1 to the next dial when the first dial changes from 9 to 0. His innovation made each digit independent of the state of the others, enabling multiple carries to rapidly cascade from one digit to another regardless of the machine's capacity. Pascal was also the first to shrink and adapt for his purpose a lantern gear, used in turret clocks and water wheels. This innovation allowed the device to resist the strength of any operator input with very little added friction.

Pascal designed the machine in 1642. After 50 prototypes, he presented the device to the public in 1645, dedicating it to Pierre Séguier, then chancellor of France. Pascal built around twenty more machines during the next decade, many of which improved on his original design. In 1649, King Louis XIV gave Pascal a royal privilege (similar to a patent), which provided the exclusive right to design and manufacture calculating machines in France. Nine Pascal calculators presently exist; most are on display in European museums.

Many later calculators were either directly inspired by or shaped by the same historical influences that had led to Pascal's invention. Gottfried Leibniz invented his Leibniz wheels after 1671, after trying to add an automatic multiplication feature to the Pascaline. In 1820, Thomas de Colmar designed his arithmometer, the first mechanical calculator strong enough and reliable enough to be used daily in an office environment. It is not clear whether he ever saw Leibniz's device, but he either re-invented it or utilized Leibniz's invention of the step drum.

Blaise Pascal began to work on his calculator in 1642, when he was 18 years old. He had been assisting his father, who worked as a tax commissioner, and sought to produce a device which could reduce some of his workload. Pascal received a Royal Privilege in 1649 that granted him exclusive rights to make and sell calculating machines in France.

By 1654 he had sold about twenty machines (only nine of those twenty machines are known to exist today), but the cost and complexity of the Pascaline was a barrier to further sales and production ceased in that year. By that time Pascal had moved on to the study of religion and philosophy, which resulted in both the Lettres provinciales and the Pensées.