Jean Baptiste Perrin, generally known as Jean Perrin (Lille, September 30, 1870 – April 17, New York, 1942), was a French physicist.

In 1895, he showed that cathode rays were made of corpuscles with negative electric charge. He computed Avogadro's number through several methods. He explained solar energy by the thermonuclear reactions of hydrogen.

Jean Perrin received the Nobel Prize in Physics in 1926 for his work on the discontinuous structure of matter, and especially for his discovery of sedimentation equilibrium.

He was the father of Francis Perrin, also a physicist.