James Mason Crafts (March 8, 1839 – June 20, 1917) was an American chemist, mostly known for developing the Friedel–Crafts alkylation and acylation reactions with Charles Friedel in 1876.

Although he never received his Ph.D., he studied chemistry in Germany at the Academy of Mines (1859) of Freiberg, and served as an assistant to Robert Bunsen at Heidelberg, and then with Wurtz in Paris (1861).

During the following four years Crafts served as professor of chemistry at the Massachusetts Institute of Technology (MIT), but in 1874 took a leave of absence, joined Friedel in Paris, and devoted himself exclusively to scientific research.

But his most important achievement was the discovery, jointly with Friedel, of one of the most fruitful synthetic methods in organic chemistry, the Friedel–Crafts reaction.

Hundreds of new carbon compounds have been brought into existence by this method (New International Encyclopedia), which is based on the catalytic action of the chloride of aluminium.