Friedrich Wilhelm Ostwald (2 September 1853–4 April 1932) was a Baltic German chemist.

Ostwald graduated from the University of Tartu, Estonia, in 1875, received his Ph.D. there in 1878 under the guidance of Carl Schmidt, and taught at Tartu from 1875 to 1881 and at Riga Polytechnicum from 1881 to 1887.
Ostwald took his doctorate from the University of Dorpat in 1878 and taught at Riga before going to the University of Leipzig (1887-1906).
He was quick to espouse the theories of Svante Arrhenius and Jacobus Henricus van't Hoff, with whom he placed physical chemistry on a firm basis. He wrote Lehrbuch der allgemeinen Chemie, 2 vol. (1885-87; "Textbook of General Chemistry") and other influential texts and was chiefly responsible for the founding (1887) of the Zeitschrift fur physikalische Chemie ("Journal of Physical Chemistry"), long the most influential publication in the field.
In 1889 he began issuing Klassiker der exakten Wissenschaften ("Classics of Exact Science"), an important series of reprints of significant papers in physics and chemistry that had appeared up to that time.
In 1894 he gave the first modern definition of a catalyst and turned his attention to catalytic reactions.
His process for the conversion of ammonia to nitric acid, patented in 1902, became of great industrial importance.
Following his resignation from Leipzig, he wrote on the philosophy of science and, in the book Grosse Manner (1909; "Great Men"), he investigated the psychological causes of scientific productivity.