George McClelland Whitesides (born August 3, 1939) is an American chemist and professor of chemistry at Harvard University. He is best known for his work in the areas of nuclear magnetic resonance spectroscopy, organometallic chemistry, molecular self-assembly, soft lithography, microfabrication, microfluidics, and nanotechnology. A prolific author and patent holder who has received many awards, he received the highest Hirsch index rating of all living chemists in 2011.

Whitesides' interests include "physical and organic chemistry, materials science, biophysics, complexity and emergence, surface science, microfluidics, optics, self-assembly, micro- and nanotechnology, science for developing economies, molecular electronics, catalysis, energy production and conservation, origin of life, rational drug design, cell-surface biochemistry, simplicity, and infochemistry." He has shifted to new research areas many times throughout his career, averaging about ten years in any particular area. Once other people successfully move into an area, he tends to look for new and more interesting problems to solve. "He has done that repeatedly by asking fundamental questions of what seemed to everyone to be virtually intractable problems," according to Jeremy R. Knowles.