Sir Geoffrey Ingram Taylor OM FRS FRSE (7 March 1886 – 27 June 1975) was a British physicist, who made instrumental contributions to fluid dynamics and wave theory.

Taylor was born in St. John's Wood, London. His father, Edward Ingram Taylor, was an artist, and his mother, Margaret Boole, came from a family of mathematicians (his aunt was Alicia Boole Stott and his grandfather was George Boole). As a child he was fascinated by science after attending the Royal Institution Christmas Lectures, and performed experiments using paint rollers and sticky-tape.

Taylor read mathematics and physics at Trinity College, Cambridge from 1905 to 1908. He won several scholarships and prizes at Cambridge, one of which enabled him to study under J. J. Thomson.

Taylor published his first paper while he was still an undergraduate. In it, he showed that interference of visible light produced fringes even with extremely weak light sources. The interference effects were produced with light from a gas light, attenuated through a series of dark glass plates, diffracting around a sewing needle. Three months were required to produce a sufficient exposure of the photographic plate. The paper does not mention quanta of light (photons) and does not reference Einstein's 1905 paper on the photoelectric effect, but today the result can be interpreted by saying that less than one photon on average was present at a time. Once it became widely accepted in around 1927 that the electromagnetic field was quantized, Taylor's experiment began to be presented in pedagogical treatments as evidence that interference effects with light cannot be interpreted in terms of one photon interfering with another photon—that, in fact, a single photon's probability amplitudes do interfere by going through both slits of a double-slit apparatus. Modern understanding of the subject has shown that the conditions in Taylor's experiment were not sufficient to demonstrate this, because the light source was not a single-photon source, but the experiment was reproduced in 1986 using a single-photon source, and the same result was obtained.

He followed this up with work on shock waves, winning a Smith's Prize. In 1910 he was elected to a Fellowship at Trinity College, and the following year he was appointed to a meteorology post, becoming Reader in Dynamical Meteorology. His work on turbulence in the atmosphere led to the publication of "Turbulent motion in fluids", which won him the Adams Prize in 1915. In 1913 Taylor served as a meteorologist aboard the Ice Patrol vessel Scotia, where his observations formed the basis of his later work on a theoretical model of mixing of the air.

At the outbreak of World War I, Taylor was sent to the Royal Aircraft Factory at Farnborough to apply his knowledge to aircraft design, working, amongst other things, on the stress on propeller shafts. He also learned to fly aeroplanes and studied the stability of parachutes.

After the war Taylor returned to Trinity and worked on an application of turbulent flow to oceanography. He also worked on the problem of bodies passing through a rotating fluid. In 1923 he was appointed to a Royal Society research professorship as a Yarrow Research Professor. This enabled him to stop teaching, which he had been doing for the previous four years, and which he both disliked and had no great aptitude for. It was in this period that he did his most wide-ranging work on fluid mechanics and solid mechanics, including research on the deformation of crystalline materials which followed from his war work at Farnborough. He also produced another major contribution to turbulent flow, where he introduced a new approach through a statistical study of velocity fluctuations.

In 1934, Taylor, roughly contemporaneously with Michael Polanyi and Egon Orowan, realised that the plastic deformation of ductile materials could be explained in terms of the theory of dislocations developed by Vito Volterra in 1905. The insight was critical in developing the modern science of solid mechanics.