John Playfair FRSE, FRS (10 March 1748 – 20 July 1819) is a Scottish scientist and mathematician, and a professor of natural philosophy at the University of Edinburgh.

He is perhaps best known for his book Illustrations of the Huttonian Theory of the Earth (1802), which summarizes the work of James Hutton.

It is through this book that Hutton's principle of uniformitarianism, later taken up by Charles Lyell, first reaches a wide audience.

Playfair is also remembered for his proposal of an alternative to Euclid's parallel postulate.