Blaise Pascal (June 19, 1623–August 19, 1662) was a French mathematician, physicist, and religious philosopher.

Pascal was a child prodigy, who was educated by his father. Pascal's earliest work was in the natural and applied sciences, where he made important contributions to the construction of mechanical calculators and the study of fluids, and clarified the concepts of pressure and vacuum by expanding the work of Evangelista Torricelli. Pascal also wrote powerfully in defense of the scientific method.

At age eighteen Pascal constructed a mechanical calculator, called Pascal's calculator or the Pascaline, capable of addition and subtraction, to help his father with this work. The Zwinger museum, in Dresden, Germany, exhibits one of his original mechanical calculators. Though these machines stand near the head of the development of computer engineering, the calculator failed to be a great commercial success. Pascal continued to make improvements to his design through the next decade and built a total of fifty machines.

Pascal's work in the fields of the study of fluids (hydrodynamics and hydrostatics) centered on the principles of hydraulic fluids. His inventions include the hydraulic press (using hydraulic pressure to multiply force) and the syringe. By 1646 Pascal had learned of Evangelista Torricelli's experimentation with barometers. Having replicated an experiment which involved placing a tube filled with mercury upside down in a bowl of mercury, Pascal questioned what force kept some mercury in the tube and what filled the space above the mercury in the tube. At the time, most scientists contended that some invisible matter was present there—not a vacuum.

Following more experimentation in this vein, in 1647 Pascal produced Experiences nouvelles touchant le vide, which detailed basic rules describing to what degree various liquids could be supported by air pressure. It also provided reasons why it was indeed a vacuum above the column of liquid in a barometer tube.

In honor of his scientific contributions, the name Pascal has been given to the SI unit of pressure, to a programming language, and Pascal's law (an important principle of hydrostatics), and as mentioned above, Pascal's triangle and Pascal's wager still bear his name.

Pascal's development of probability theory was his most influential contribution to mathematics. Originally applied to gambling, today it is extremely important in economics, especially in actuarial science.

In literature, Pascal is regarded as one of the most important authors of the French Classical Period, and is read today as one of the greatest masters of French prose.