André-Marie Ampère (1775-1836) was a French physicist who discovered the laws of electromagnetism. Ampère made his discoveries in the 1820's, encouraged by the Danish physicist Hans Christian Oersted's 1820 observation that a magnetic needle is deflected when placed near a wire carrying current. Ampère's experiments showed that parallel electric currents moving in the same direction attract each other, while those moving in opposite directions repel each other. From these and similar observations, Ampère developed a mathematical theory that described the relationship of a magnetic field to the electric current that produces it, now known as Ampère's Law.

Further discoveries led to the invention of the galvanometer, an instrument used for measuring electric current. Ampère found that applying an electric current to a coiled wire makes the wire behave like a magnet. He used this scientific phenomenon to develop the galvanometer.

Ampère was a child prodigy who had mastered mathematics by the time he was a teenager and was made a professor at 26. In 1809 he became professor of mathematics at the École Polytechnique Institute in Paris. For all of his life, Ampère's approach to science was to follow a flash of inspiration then work to a conclusion rather than to work methodically.

Ampère published his work on electromagnetism, Mathematical Theory of Electrodynamic Phenomena in 1827. Ampère is honored by the standard unit of electric current measurement, the ampere.