Aaron Klug (born Zelvas, Lithuania, August 11 1926) is a Lithuanian-born British physicist and chemist, and winner of the 1982 Nobel Prize in Chemistry for his development of crystallographic electron microscopy.

Having moved to South Africa at the age of two, he graduated with a degree in science at the University of Witwatersrand and studied crystallography at the University of Cape Town before moving to England, completing his doctorate at Trinity College, Cambridge in 1953.

Working with Rosalind Franklin in John Bernal's in London aroused a lifelong interest in the study of viruses, and during his time there in the late 1950s made discoveries in the structure of the tobacco mosaic virus. Over the following decade Klug used methods from X-ray diffraction, microscopy and structural modelling to develop crystallographic electron microscopy in which a sequence of two-dimensional images of crystals taken from different angles are combined to produce three-dimensional images of the target.

Between 1986 and 1996 he was director of the Laboratory of Molecular Biology in Cambridge, and was knighted in 1988.